ott- 


mthern  Brand 
of  the 

University  of  California 

Los  Angeles 

FormL  1 

QC 


This  book  is  DUE  on  the  last  date  stamped  below 


JUL 


L-9-15m-8,'26 


^ 


SCIENCE  FOR  THE  YOUNG; 

OR, 

THE  FUNDAMENTAL  PRINCIPLES  OF  "MODERN  PHILOSOPHY 
EXPLAINED  AND  ILLUSTRATED 

IN 
CONVERSATIONS  AND  EXPERIMENTS, 

AND   IN 

NARRATIVES  OF  TRAVEL  AND  ADVENTURE  BY  YOUNG 
PERSONS  IN  PURSUIT  OF  KNOWLEDGE. 


VOL.  IV.— FORCE. 


t/ 
SCIENCE  FOR  THE  YOUNG. 


FORCE. 


BY  JACOB  ABBOTT, 


AUTHOR  OF 


'THE  FRANCONIA  STORIES,"    "MARCO  PAUL  SERIES,"   "YOUNG 

CHRISTIAN   SERIES,"    "HARPER'S    STORY   BOOKS," 

"ABBOTT'S  ILLUSTRATED  HISTORIES,"  &c. 


WITH  NUMEROUS  ENGRA  VINGS. 


NEW    YORK: 

HARPER  &  BROTHERS,  PUBLISHERS, 

FRANKLIN     SQUARE. 


NOV 


Entered  according  to  Act  of  Congress,  in  the  year  1872,  by 

HARPER  &   BROTHERS, 

In  the  Office  of  the  Librarian  of  Congress,  at  Washington, 


A  y£) 

OBJECT  OF  THE  WORK. 

THE  object  of  this  series,  though  it  has  been  prepared 
with  special  reference  to  the  young,  and  is  written  to  a 
considerable  extent  in  a  narrative  form,  is  not  mainly  to 
amuse  the  readers  with  the  interest  of  incident  and  ad- 
venture, nor  even  to  entertain  them  with  accounts  of  cu- 
rious or  wonderful  phenomena,  but  to  give  to  those  who, 
though  perhaps  still  young,  have  attained,  in  respect  to 
their  powers  of  observation  and  reflection,  to  a  certain 
degree  of  development,  some  substantial  and  thorough 
instruction  in  respect  to  the  fundamental  principles  of 
the  sciences  treated  of  in  the  several  volumes.  The  pleas- 
ure, therefore,  which  the  readers  of  these  pages  will  de- 
rive from  the  perusal  of  them,  so  far  as  the  object  which 
the  author  has  in  view  is  attained,  will  be  that  of  under- 
standing principles  which  will  be  in  some  respects  new 
to  them,  and  which  it  will  often  require  careful  attention 
on  their  part  fully  to  comprehend,  and  of  perceiving  sub- 
sequently by  means  of  these  principles  the  import  and 
significance  of  phenomena  occurring  around  them  which 
had  before  been  mysterious  or  unmeaning. 

In  the  preparation  of  the  volumes  the  author  has  been 
greatly  indebted  to  the  works  of  recent  European,  and 
especially  French  writers,  both  for  the  clear  and  succinct 
expositions  they  have  given  of  the  results  of  modern  in- 
vestigations and  discoveries,  and  also  for  the  designs  and 
engravings  with  which  they  have  illustrated  them. 


CONTENTS. 


I.  RICK   VAN  DORN 13 

II.  CRANK   MOTION 21 

III.  MECHANICAL   FORCE 3C 

IV.  TRANSFER  OF   FORCE    BY    PULLETS   AND   BANDS 50 

V.  TRANSFER   OF   FORCE  BY   GEARING 58 

VI.  THE   MILL 73 

VII.  FALLING   FORCE 90 

VIII.  HEAT 108 

IX.  THE   FOUR   CIRCUITS   OF   SOLAR   ENERGY 123 

X.  THE   FOUR   CIRCUITS   OF   SOLAR   ENERGY 146 

XI.  THE   FOUR   CIRCUITS   OF   SOLAR   ENERGY 172 

XII.  THE   FOUR   CIRCUITS   OF   SOLAR   ENERGY "191 

XIII.  SCIENCE   AND   SENTIMENT 223 

XIV.  THE   SUN 236 

XV.  RICK   AGAIN 264 

XVI.  DETONATIONS   AND    EXPLOSIONS 276 

XVII.  FORCE    IN   RELATION   TO   TIME 289 

XVIII.  CONCLUSION 302 


ILLUSTRATIONS. 

Lawrence's  Seat   Frontispiece. 

Liquefaction 16 

Force  of  the  Wind 27 

Crank  Motion 30 

Iron  Shears 36 

A  Primitive  Lathe 39 

The  Bow-lathe 42 

Rick  at  the  Lathe 47 

Open  Belt 52 

Crossed  Belt 52 

Fast  and  loose  Pulleys 52 

Burnishing  Marble  Paper 53 

Axis  at  right  Angles. rA 

Pulleys  of  different  Sizes 55 

Means  of  varying  Speed  and  Power.  56 

Gearing 58 

Variable  Speed 59 

Complicated  Movement 60 

Barrel  and  Fusee 61 

Crown  Wheel 62 

Beveled  Wheels 62 

Hack  and  Pinion 63 

Reciprocating  Movement 63 

Forward  and  Reverse  Motion 63 

Chain  and  Pulley 64 

Another  Form 64 

Single-toothed  Wheels 64 

Eccentric,  or  Cam 65 

Action  of  the  Cam 65 

Wipers 66 

Wipers  again 66 

Crank-pin 66 

The  first  Locomotive 67 

Automatic  Action 68 

WTings  without  Force  to  work  them 70 

More  Wings  without  Force 71 

Making  a  Sluice-way 78 

Undershot  Wheel 82 

Overshot  Wheel 85 


Xll  ILLTJSTKATIONS. 

Page 

The  Pile-driver.. .   100 

The  Mill-pond 103 

A  King-post 106 

Fire  by  Friction Ill 

Holy  Fire 112 

Work  of  the  Sun 124 

The  Hurricane 134 

The  Anemometer 136 

Pressure  of  twenty  Pounds  per  Foot 140 

Pressure  of  the  Wind 141 

The  Water-spout 143 

Clouds :  Primary  Forms T.  ..  r ,. .  'r 154 

Clouds  :  Secondaiy  Forms..?!!1.  ,.M . ...7..? 158 

Self-registering  Pluviameter 166 

Expenditure  of  Falling  Force   , 170 

Contending  Radiations 175 

Field  Ice ._ 178 

Eifects  of  the  Avalanche .-.r-.....' 186 

Scenery  on  the  Coast  of  Norway 188 

Among  the  Icebergs  after  Seals  and  Whales 1 89 

Stomata 193 

Section  of  a  Stoma 193 

Solar  Force  restored 198 

Contending  Currents  of  Solar  Energy.    Victory  easy 202 

Victory  doubtful 205 

The  Sun  giving  Help 216 

The  Sun  sending  Warning 219 

Appearance  during  a  total  Eclipse 245 

The  Helioscope 248 

General  Appearance  of  Spots 249 

Appearances  indicating  Cavities 250 

Mottled  Surface.     Willow  Leaves.     Luminous  Bridges 253 

Changes  of  Form 255 

The  Meteor 261 

The  Zodiacal  Light 262 

We're  resting 272 

Measuring  the  Bursting  Pressure 282 

Transmitting  an  Impulse  of  Force 295 

Oblique  Action 298 

The  Torsion  Balance ...  ..  299 


FORCE. 


/  O 


CHAPTER  I. 

KICK  VAN   DORN. 

"  JOHN,"  said  Lawrence  one  day,  when  John  was  with 
him  in  the  shop  watching  some  work  at  the  lathe  in  which 
he  was  engaged,  "  are  there  any  bad  boys  in  your  school  ?" 

"  Two  or  three,"  said  John. 

"Is  there  any  one  that  is  really  ugly,"  continued  Law- 
rence, "  so  that  every  body  dislikes  him  ?  I  want  a  really 
ugly  boy." 

"There's  Rick  Van  Dora,"  said  John.  "He's  ugly 
enough.  But  what  do  you  want  of  an  ugly  boy  ?" 

"  I  wish  to  try  some  experiments  upon  him,"  said  Law- 
rence. 

"  Oh  ho  !"  exclaimed  John.  "  What  an  idea !  You  can't 
try  experiments  upon  a  boy." 

"  I  want  to  see,  at  any  rate,  whether  I  can  or  not,"  said 
Lawrence.  " How  old  a  boy  is  Rick,  as  you  call  him?" 

"  About  twelve  or  fourteen,"  said  John. 


14  RICK   VAN   CORN. 

"How  came  he  by  such  a  name  as  Rick?"  asked  Law- 
rence. 

"  I  don't  know,"  replied  John.  "  His  real  name  may  be 
Richard,  for  aught  I  know.  But  the  boys  always  call  him 
Rick." 

"Is  he  a  handsome  boy?"  asked  Lawrence. 

"  No,"  said  John.  "  He  looks  as  cross  and  ugly  as  he  is. 
All  the  boys  despise  him  and  hate  him.  Besides,  he  is  the 
poorest  scholar  in  school.  Pie  don't  study  any,  and  he  is 
always  in  some  mischief  or  other." 

"  Doesn't  he  do  any  thing  well  ?"  asked  Lawrence. 

"He  plays  ball  pretty  well,"  said  John.  "Yes,  he's  a 
good  ball-player.  They  all  like  to  have  him  on  their  side 
in  playing  ball,  and  I  don't  believe  but  that  he  might  do 
well  in  other  things  if  he  only  would  try ;  but  he  won't 
try." 

"  Well,  couldn't  you  ask  him  to  come  here  and  see  me 
some  day  ?"  said  Lawrence. 

"He  wouldn't  come  if  I  should  ask  him,"  replied  John. 

"  Why  not?"  asked  Lawrence. 

"  He  would  think  that  you  had  some  design  upon  him," 
said  John.  "  He  is  very  suspicious  when  any  body  sends 
for  him.  He  thinks,  I  suppose,  that  he  is  going  to  get  a 
scolding  for  some  of  his  misdeeds." 

"Tell  him,"  said  Lawrence,  "  that  I  have  got  a  lathe,  and 
am  going  to  turn  a  bat,  and  that  I  want  him  to  come  and 
tell  me  about  the  best  size  and  shape  of  it" 

"He  may  possibly  come  for  that,"  said  John,  musingly; 
"  but  he  is  more  likely  to  think  that  it  is  only  a  pretense — 
to  catch  him." 

"  Well,  I  must  confess  he  would  not  be  far  from  right  in 
that  supposition,"  said  Lawrence.  "  But  you  can  ask  him, 
at  any  rate.  Ask  him  to  come  next  Saturday  forenoon." 

"  Well,"  said  John, "  I'll  ask  him,  though  it  is  very  doubt- 


NATURE    OF   OUR   KNOWLEDGE.  15 

ful  whether  he  will  come.  But  what  do  you  really  want 
him  for,  any  how  ?" 

"  I  want  to  try  an  experiment  upon  him.  I'm  going  to 
try  to  reform  him." 

"  To  reform  him  !"  repeated  John.  "  I'm  sure  you  won't 
succeed.  Every  thing  has  been  tried  already  and  failed. 
I  should  like  to  know  by  what  means  you  expect  to  reform 
him." 

"By  means  of  force,"  said  Lawrence,  quietly. 

"Force!  Hoh  !"  exclaimed  John,  much  surprised.  "I 
don't  think  you  have  any  authority  to  use  force  upon  him. 
Besides,  he  won't  stay.  And  then  force  has  been  used.  He 
says  that  if  there  was  any  virtue  in  whipping  to  make  a 
good  boy,  he  should  have  been  a  saint  before  this  time,  for 
he  has  had  nothing  but  whippings  all  his  life." 

"I  did  not  express  myself  quite  right,"  said  Lawrence. 
"  It  is  not  force  itself  exactly,  but  ideas  offeree  that  I  mean 
to  employ.  But  you  persuade  him  to  come,  and  I'll  try 
my  experiment ;  and  I'll  explain  to  you,  in  the  end,  how  it 
worked." 

And  here  it  must  be  said  that  there  is  one  thing  curious 
in  respect  to  our  ideas  of  every  thing  pertaining  to  the  ex- 
ternal world,  and  that  is,  that  we  can  not,  strictly  speaking, 
form  any  conception  of  what  any  thing  really  is,  in  its  in- 
trinsic and  real  essence,  but  only  how  it  acts. 

To  show  what  I  mean  by  this,  let  us  take  the  case  of  lead 
as  an  example.  "We  say  that  lead  is  heavy.  We  mean 
by  that  that  when  we  let  it  rest  upon  our  hand,  or  upon 
any  movable  support,  it  weighs  it  down ;  that  is,  it  acts  in 
a  certain  way.  We  say  it  is  malleable ;  we  mean  nothing 
more  by  that  than  that  when  it  is  struck  by  any  hard  sub- 
stance it  yields,  and  becomes  indented  or  flattened.  It  is 
fusible,  which  is  only  a  word  expressing  how  it  acts  when 
heated  to  a  certain  degree,  namely,  it  sinks  down  from  its 


10 


KICK   VAN   DOEN. 


EFAOT1ON. 


solid  state  and  gradually  becomes  liquid.  When  we  say 
it  is  of  a  bluish  color,  we  mean  simply  that  when  it  is 
held  before  our  eyes  it  sends  rays  of  light  into  them  which 
produce  in  our  minds  a  particular  sensation.  It  is  the  same 
with  all  the  other  properties  of  lead.  The  names  of  these 
properties  are  only  expressions  of  the  manner  in  which  the 
substance  acts  under  different  specified  circumstances. 

As  to  the  substance  itself  in  its  intrinsic  and  absolute 
nature  we  can  have  no  idea  whatever. 

Now  it  is  not  only  so  with  lead  and  other  metals,  but 
with  all  the  material  substances,  and  all  the  agencies  and 
powers  of  nature  of  every  kind.  What  we  call  force  forms 


LAWRENCE'S  REFLECTIONS.  17 

no  exception  to  this  universal  rule.  There  is  something  in 
its  inner  and  intrinsic  nature  that  entirely  eludes  the  efforts 
of  the  wisest  philosophers  to  comprehend.  All  that  we  can 
really  learn  about  it  is  how  it  acts.  The  young  persons, 
therefore,  who  may  read  this  book,  must  give  up  all  idea  of 
obtaining  from  it  any  conception  of  what  force,  in  its  hidden 
nature,  is,  and  only  hope  to  learn  in  what  different  forms  it 
presents  itself  to  us,  and  in  what  ways  it  acts  in  those  dif- 
ferent forms. 

And  so  Lawrence,  in  saying  that  he  was  going  to  try  to 
interest  Rick  Van  Dorn  in  ideas  of  force,  meant  only  that  he 
intended  to  try  to  interest  his  mind  in  certain  new  trains 
of  thought  in  respect  to  the  different  forms  of  force,  and 
its  various  modes  of  action,  and  not  at  all  in  relation  to  its 
internal  and  absolute  nature. 

The  fact  was,  that  Lawrence  had  become  so  accustomed, 
in  his  scientific  studies,  to  consider  all  the  substances  and 
agencies  in  nature  as  governed  by  fixed  laws,  so  that  the 
way  to  change  the  action  of  any  one  of  them  was  to  change 
the  circumstances  under  which  it  was  placed,  and  not  to 
get  out  of  patience  and  fret  at  the  wrong  action — as,  for 
example,  if  he  was  trying  to  melt  lead,  and  it  would  not 
melt  as  fast  as  he  expected,  not  to  denounce  or  find  fault 
with  the  lead,  but  simply  and  quietly  to  give  it  more  time, 
or  apply  more  heat — he  had  become  so  accustomed,  I  say, 
to  act  on  these  principles  in  dealing  with  material  agencies, 
that  he  was  quite  inclined  to  look  upon  mental  and  moral 
processes  in  somewhat  the  same  light.  Or,  rather,  he  was 
inclined  to  consider  and  inquire  whether  there  might  not 
be  something  analogous  in  the  phenomena  of  mind  to  the 
regularity  of  sequence,  in  respect  to  cause  and  effect,  that 
he  knew  so  certainly  every  where  prevailed  in  the  world 
of  matter. 

There  can  be  no  doubt,  I  think,  that  there  is  some  truth 


18  KICK   VAN   BORN. 

in  this  view  of  the  subject,  and  that  AVC  should  all  act  move 
philosophically,  and  get  on  much  better,  in  dealing  with  the 
wrong  doing  that  we  witness  around  us  in  the  world,  if  we 
would  scold  and  fret  about  it  less,  and  be  less  inclined  to 
be  made  indignant  by  it,  and  try  more  to  devise  means  for 
changing  the  influences  that  have  been  or  are  now  oper- 
ating upon  those  that  act  badly. 

But  we  must  return  to  Lawrence  and  John. 

"But  really,"  said  John,  after  a  short  pause,  what  kind 
of  an  experiment  is  it  that  you  are  going  to  try  on  Rick?" 

"I  can't  explain  it  very  well,"  said  Lawrence,  "  till  after 
I  have  tried  it.  But  I'll  tell  you  a  little  story  which  per- 
haps you  may  think  will  throw  some  light  upon  it." 

So  Lawrence  began  his  story  as  follows : 

"  There  was  once  a  farmer  who  was  worried  and  plagued 
almost  to  death  by  a  swampy  place  on  his  meadow.  There 
was  a  little  rill  of  water  which  came  down  from  a  spring 
on  the  upland,  and,  instead  of  finding  a  natural  channel  by 
which  it  could  flow  off  into  the  river,  it  spread  all  over  the 
ground  in  a  certain  spot,  and  killed  out  all  the  healthy 
grass,  and  caused  hummocks  of  wild  grass  and  weeds  to 
grow  in  its  place.  It  made  the  ground  so  soft  and  boggy 
that  the  farmer  sank  into  it  over  his  shoes,  even  when  he 
went  near  the  margin  of  it ;  and  his  cattle  often  got  mired 
in  it.  The  farmer  used  to  fret  and  scold  every  time  he 
came  that  way,  saying, '  Confound  the  vile  brook !' 

"  At  one  time  he  conceived  the  idea  of  curing  the  mis- 
chief, by  stopping  the  water  from  coming  into  the  meadow 
by  a  dam.  So  he  hauled  a  great  log  across  the  little  rill 
where  it  came  down  from  the  upland,  and  by  packing  sods 
against  the  upper  side  of  the  log  he  made  quite  a  good 
dam.  But  of  course  the  dam  soon  got  full,  the  water  ran 
over  the  top  of  the  log,  or,  insinuating  itself  among  the 
sods,  oozed  through,  and  soon  made  the  matter  worse  than 


FOOLISH   MANAGEMENT.  19 

before.  Then  he  tried  another  dam  a  little  farther  up,  and 
afterward  another  a  little  farther  down,  but  all  to  no  effect." 

"  What  a  silly  man  !"  said  John. 

"He  used  to  complain  in  an  impatient  and  fretful  way 
to  his  wife  and  to  his  neighbors  about  the  plaguy  brook," 
continued  Lawrence.  "  It  was  the  torment  of  his  life,"  he 
said.  He  did  not  dare  even  to  let  his  children  go  into  the 
field  for  fear  that  they  should  get  swamped  in  that  quag- 
mire. 

"At  last  one  of  his  neighbors  went  with  him  to  look  at 
the  place. 

"'Why,  man,'  said  his  neighbor,  'you  don't  go  to  work 
in  the  right  way.  You  must  not  fight  the  mischief  by 
damming  up  the  flow  of  the  water,  but  you  must  open  a 
channel  for  it  in  a  safe  place  where  it  will  do  no  mischief.' 

"So  his  neighbor  helped  him  to  tear  away  one  of  the 
little  dikes  which  he  had  made  on  one  side,  to  prevent  the 
water  from  spreading  over  a  new  place  in  the  meadow, 
and  dug  a  channel  in  the  ground  where  the  dam  had  been. 
They  continued  this  channel  down  through  the  part  of  the 
ground  most  favorable  till  they  reached  the  river.  As 
soon  as  they  had  done  this,  the  water  began  to  flow  freely 
through  it.  The  farmer  and  his  neighbor  looked  at  the 
little  rill  a  few  minutes,  and  then  the  farmer  turned  toward 
the  swampy  place  and  said, '  It  doesn't  do  a  bit  of  good. 
The  ground  there  is  just  as  miry,  and  the  grass  as  coarse 
and  good  for  nothing  as  ever.' 

" '  My  dear  man,'  said  the  neighbor, '  do  you  expect  the 
mischief  that  has  been  years  in  growing  can  be  repaired 
in  an  hour?  Wait  three  months  and  then  see.' 

"  The  farmer  waited  three  months,  and  by  that  time  the 
aspect  of  things  had  entirely  changed.  The  swampy  place 
had  become  of  itself  dry  and  hard,  and  the  cultivated 
grasses,  good  for  hay,  had  spread  all  over  it  again,  and  the 


20  KICK   VAN   DOKN. 

water  flowed  quietly  down  toward  the  river  through  a 
pretty  winding  channel  over  a  sandy  bottom,  and  between 
banks  of  flowers,  where  the  farmer's  children  used  to  like 
to  come  often  to  play." 

Lawrence  paused  as  if  he  had  finished  his  story.  John 
also  paused  a  moment  or  two,  as  if  he  were  thinking  of  it. 

"  It  is  a  very  good  story,"  he  said  at  length,  "  though  I 
don't  see  what  it  has  to  do  with  your  plan  about  Rick  Van 
Dorn.  You  said  it  would  throw  some  light  on  that  sub- 
ject." 

"  I  said  perhaps  you  would  think  that  it  threw  some  light 
on  that  subject,"  said  Lawrence. 

"  I  don't  think  it  does,"  said  John.  "  At  least  I  don't  see 
any  light." 

"  Then  I  was  mistaken,"  said  LaAvrence. 


KICK   ON   HIS   GUARD.  21 


CHAPTER  II. 

CRANK    MOTION. 

LAWRENCE  and  John  were  at  a  town  in  New  England, 
near  the  sources  of  the  Connecticut  River,  where  Lawrence 
was  pursuing  some  scientific  studies  connected  with  his 
profession  of  civil  engineer,  and  John  was  receiving  in- 
struction at  a  certain  institution  in  the  vicinity,  known  as 
the  Morningside  school,  at  the  time  when  the  conversation 
described  in  the  preceding  chapter  took  place. 

Lawrence  had  fitted  himself  up  a  shop,  where  he  had  a 
bench  and  tools,  and  also  a  lathe,  and  where  he  was  accus- 
tomed to  work  at  leisure  times,  making  apparatus  of  various 
kinds  for  his  investigations  and  experiments.  It  was  to 
this  shop  that  he  invited  Rick  to  come. 

On  the  Saturday  following  the  conversation  narrated  in 
the  last  chapter,  John  came  into  the  shop  where  Lawrence 
was  at  work,  and  said  that  Rick  had  come  to  the  gate,  but 
would  not  come  in. 

"  "Why  won't  he  come  in  ?"  asked  Lawrence. 

"  I  don't  know,"  replied  John.  "He  seems  to  think  that 
you  have  some  design  upon  him." 

So  Lawrence  went  out  to  the  door  and  called  to  Rick. 

"  Rick,"  said  he,  "  come  in  here." 

"  What  do  you  want  of  me  ?"  asked  Rick. 

"I  want  you  to  give  me  some  advice  about  making  a 
bat,"  said  Lawrence. 

Rick,  who  was  standing  just  outside  of  a  gateway,  with 
his  hand  upon  the  gate,  as  if  ready  to  start  off  at  the  least 


22  CRANK   MOTION. 

alarm,  looked  curiously  upon  Lawrence  for  a  moment,  and 
then  said, "  Upon  honor  ?" 

"  Yes,"  said  Lawrence,  "  upon  honor." 

"You  have  got  some  secret  design  upon  me,  I  believe," 
said  Rick. 

"That's  a  fact,"  said  Lawrence;  "  I  have." 

Rick  looked  up  surprised. 

"What  is  it?"  said  he. 

"  To  make  you  my  friend,"  replied  Lawrence,  "  so  that 
you  will  come  here  often  and  help  me." 

Rick  looked  surprised  and  puzzled.  He  gazed  a  moment 
at  Lawrence  as  if  uncertain  what  to  do,  and  then,  as  if  won 
by  Lawrence's  frank  and  open  expression  of  countenance, 
and  his  honest  and  friendly  manner,  he  came  slowly  toward 
him  and  entered  the  shop. 

He  and  Lawrence  had,  however,,  scarcely  entered  the 
shop  before  a  messenger  came  from  the  house  to  say  that 
some  visitors  had  called,  and  Lawrence  and  John  were  re- 
quested to  go  in  and  see  them.  So  Lawrence  asked  Rick 
to  excuse  him  for  a  few  minutes. 

"  You  can  amuse  yourself,"  said  he, "  in  looking  about  the 
shop  while  we  are  gone,  and  seeing  the  tools  and  things." 

So  Lawrence  and  John  went  away.  As  they  were  going 
along  the  passage-way  that  led  into  the  house,  John  said 
to  Lawrence, 

"  I  don't  think  much  of  your  sense  in  leaving  such  a  boy 
as  Rick  among  your  nice  tools." 

"Why — what  will  he  do?"  asked  Lawrence. 

"  Oh,  he'll  do  some  mischief  or  other,"  replied  John. 
"He'll  break  something,  or  dull  some  tool,  or  play  some 
trick  or  other." 

"  I  hope  he  will,"  said  Lawrence. 

"Hope  he  will !"  exclaimed  John,  surprised.  "  Why  do 
you  hope  he  will  ?" 


RICK'S  DOINGS.  23 

"Because  then  I  shall  know  that  he  is  really  the  kind  of 
boy  that  I  want  to  experiment  upon,"  said  Lawrence. 

Lawrence's  wishes,  thus  expressed,  were  not,  however, 
after  all,  exactly  realized,  for  Rick,  when  left  alone  in  the 
shop,  did  not  undertake  to  do  any  actually  malicious  mis- 
chief, though  he  met  with  a  mishap  which  for  a  moment 
greatly  alarmed  him.  It  happened  that  there  was  a  grind- 
stone in  the  corner  of  Lawrence's  shop  which  was  turned 
by  means  of  what  is  called  a  treadle.  Such  a  treadle  con- 
sists of  a  wooden  bar  placed  near  the  ground  parallel  to 
the  frame  of  the  grindstone.  The  end  which  is  farthest 
from  the  grinder  when  the  stone  is  in  use  is  pivoted  to 
the  frame  by  means  of  a  wooden  pin,  and  to  the  middle  of 
it  is  attached  an  iron  rod  which  extends  upward,  and  by 
means  of  a  hook  at  the  upper  end  clasps  a  small  crank 
formed  upon  the  axle  of  the  grindstone,  while  the  other 
end  extends  forward  near  the  place  where  the  grinder 
stands.  By  this  contrivance  the  grinder,  working  this 
outer  end  of  the  bar  with  his  foot,  can  turn  the  grindstone 
himself,  while  holding  the  tool  with  his  hands,  so  as  to  ob- 
viate the  necessity  of  having  two  persons  to  do  the  work. 

Now  Rick,  in  seeing  this  grindstone  standing  in  the 
corner,  went  to  it,  and,  as  idle  boys  are  always  very  prone 
to  do  in  such  cases,  began  turning  it  around  by  means  of 
the  treadle,  by  way  of  amusing  himself,  to  see  how  fast  he 
could  make  it  spin. 

So  he  began  to  work  the  treadle  with  his  foot,  bearing 
hard  upon  the  outer  end  of  it  with  his  whole  weight  every 
time  the  crank  came  round,  thus  imparting  to  it  a  rapidly 
increasing  motion.  In  a  short  time  the  heavy  stone  was 
brought  into  a  state  of  very  swift  rotation,  and  it  revolved, 
moreover,  with  so  much  power  that  the  crank,  in  turning, 
would  lift  the  outer  end  of  the  treadle-bar  so  forcibly  as  to 
lift  Rick  off  the  ground  when  he  rested  his  weight  upon  it, 


24  CRANK   MOTION. 

and  give  him  what  he  called  a  ride.  But  the  fun,  as  Rick 
called  it,  was  soon  brought  to  a  very  unexpected  termina- 
tion by  something  suddenly  giving  way.  The  treadle-bar 
flew  out  of  its  place,  the  connecting  rod  became  separated, 
and  the  different  parts  flew  about  in  the  most  violent  and 
alarming  manner  as  the  stone  went  whirling  round  with 
great  apparent  momentum.  Rick  was  aghast  with  sur- 
prise and  alarm.  He  seized  hold  of  the  stone  and  tried  to 
stop  its  motion.  But  all  his  efforts  were  vain.  It  went 
furiously  on,  and  seemed  to  be  rattling  and  smashing  every 
thing  to  pieces. 

It  was  just  at  this  crisis  that  Lawrence  and  John  came 
back  into  the  shop.  Rick  was  much  alarmed.  He  looked 
up  toward  Lawrence  as  he  saw  him  coming  in,  and  said, 

"Dear  me  !  I've  done  some  dreadful  mischief!" 

"Oh  no!"  said  Lawrence.  "You  may  have  done  some 
damage,  but  I  do  not  believe  you  have  done  any  mischief. 
Mischief  is  harm  done  intentionally,  and  I  am  sure  you  can 
not  have  intended  to  do  any  harm  to  my  things." 

Rick  said  that  he  would  not  do  damage  on  purpose  on 
any  account. 

Lawrence  then  went  to  examine  the  grindstone,  and  after 
looking  at  it  a  moment  as  it  gradually  ceased  its  motion 
and  came  to  a  stand-still,  he  said, 

"  You  have  not  even  done  any  damage — at  least,  none  of 
any  consequence.  There  was  only  a  pin  that  came  out.  It 
ought  to  have  been  fastened  in  more  securely." 

Rick  was  quite  reassured  by  hearing  Lawrence  speak  of 
the  damage  which  he  had  done  in  this  way,  and  began  at 
once  to  help  Lawrence  to  repair  it.  The  pin  that  had  come 
out  was  in  the  farther  end  of  the  treadle-bar,  and  was  the 
pivot  on  which  that  end  turned  in  working  the  treadle,  so 
as  to  cause  the  grindstone  to  revolve. 

"You  have  not  only  not  done  any  damage,"  said  Law- 


ACCUMULATION    OF   FORCE.  25 

rencc,  but  you  have  performed  an  experiment  that  illus- 
trates a  very  fundamental  principle  in  respect  to  the  nature 
of  force.  I  will  explain  the  principle  to  you,  and  if  you 
and  John  understand  it,  and  remember  it,  you  will  gain  a 
great  deal  more  good  from  the  accident  than  it  will  occa- 
sion me  of  trouble  in  repairing  the  damage." 

Lawrence  went  on  to  say  that  the  principle  which  he 
referred  to  was  this:  That  force  was  an  agency  that  ex- 
isted always  in  definite  and  measurable  quantities,  such 
that,  though  it  might  be  transferred  from  one  place  of  de- 
posit to  another,  and  so  be  accumulated  or  dispersed,  it 
could  not  in  any  way  be  increased  or  diminished. 

"  Yes,"  said  John,  "  it  can  be  increased ;  for  when  your 
grindstone  was  spinning  round  very  fast,  it  exerted  a  great 
deal  more  force  than  Rick  did  by  the  power  of  his  foot," 

"It  exerted  more  force  in  any  one  instant"  said  Law- 
rence, "  than  Rick  could  exert  in  that  instant ;  but  the 
whole  amount  of  all  the  impulses  that  Rick  gave  to  it  was 
equal  to  all  that  the  grindstone  could  exert ;  that  is,  there 
was  in  the  stone  an  accumulation  of  a  great  many  small 
forces,  and  not  any  increase  of  the  whole  amount. 

"It  was  like  filling  a  pail  with  water  by  pouring  in  a  great 
many  mugsful  from  a  spring,"  continued  Lawrence.  "It 
is  true,  you  may  increase  the  quantity  that  is  in  the  pail, 
and  in  that  sense  we  may  say  there  is  an  increase;  but 
there  is  no  actual  increase  on  the  whole,  for  the  amount 
that  is  in  the  pail,  when  it  is  full,  is  only  made  up  of  the 
separate  amounts  of  all  the  dipperfuls.  There  can  not 
be,  absolutely,  in  the  whole  amount,  any  increase  or  dimi- 
nution." 

"There  might  be  a  diminution,"  said  John,  "for  some 
of  the  water  might  be  spilled." 

"True,"  replied  Lawrence,"  a  part  might  be  spilled,  and 
a  part  might  dry  up ;  but  none  of  it  would  cease  to  exist 
B 


20  CRANK    MOTION. 

on  that  account.  Wherever  it  went  when  it  was  spilled, 
or  wherever  the  vapor  went  of  that  which  was  turned  into 
vapor,  there  it  would  be.  There  might  be  a  diminution  of 
the  quantity  in  the  pail,  but  there  could  be  no  diminution 
of  the  actual  amount  of  water  employed  in  the  experiment. 
Precisely  the  same  amount,  neither  any  more  nor  any  less, 
would  exist  somewhere  at  the  end  of  the  experiment  that 
existed  at  the  beginning. 

"And  it  is  just  so  in  respect  to  force,"  continued  Law- 
rence. "Precisely  the  same  quantity  that  we  have  at  the 
commencement  of  any  process,  or  at  the  entrance,  so  to 
speak,  of  any  combination  of  machinery,  exists  somewhere 
at  the  end  of  the  process ;  or,  in  the  case  of  machinery,  must 
be  stored  in  it,  or  must  issue  from  it  in  some  way.  There 
can  not  possibly  be  any  real  gain  or  loss  of  force  any  more 
than  there  can  be  of  water.  A  great  many  small  or  gentle 
forces  may  be  combined  to  make  a  great  one,  and,  on  the 
other  hand,  a  great  one  may  be  subdivided  into  many  small 
ones,  but  there  can  not,  in  either  case,  be  any  absolute  in- 
crease or  diminution  of  the  amount. 

"Take,  for  example,  the  case  of  wind  blowing  the  trees,  as 
shown  in  the  engraving.  Nothing  can  seem,  at  first  view, 
more  vague  and  indefinite  than  such  a  force  as  this,  and 
yet  nothing  can  be  more  strictly  defined  and  determinate 
in  its  nature  than  the  action  of  the  breeze  in  such  a  case 
really  is.  For  every  leaf,  and  for  the  area  of  every  branch 
and  stem,  there  is  a  certain  stream  of  particles  of  air,  each 
moving  with  a  certain  definite  velocity,  and  all  consequent- 
ly striking  against  the  leaf  or  the  stem  with  a  certain  force ; 
so  that,  if  the  quantity  of  air  in  one  of  the  streams,  and  the 
rate  of  its  motion,  were  known,  the  precise  amount  of  the 
force  which  it  would  exert  would  be  determined.  Each 
particle  strikes  with  a  definite  force,  depending  upon  its 
weight  and  its  rate  of  motion,  and  this  amount  of  force 


PERSISTENCE    OF   FORCE.  29 

can  not  be  made  either  less  or  more  while  those  conditions 
remain  unchanged. 

"  Thus  every  force  which  we  see  acting  in  nature  around 
us  exists  in  precise  and  definite  quantities,  which  can  in- 
deed be  made  to  pass  from  one  body  into  another,  and  in 
that  way  can  be  accumulated,  and  can  be  made  to  change, 
too,  from  one  form  into  another,  as  will  be  more  fully  ex- 
plained hereafter ;  but  the  amount  can  never  be  increased 
in  any  other  way  than  by  uniting  a  great  many  small  forces 
into  a  larger  one,  or  diminished  in  any  other  way  than  by 
dividing  a  large  one  into  many  small  ones,  in  neither  of 
which  cases  is  there  any  absolute  increasing  or  diminishing 
of  the  absolute  amount. 

"  It  results  from  this,  that  whenever  we  see  any  force, 
however  great,  in  action,  as,  for  example,  in  the  case  of 
a  windmill  turning  with  great  speed,  or  a  steam-engine 
driving  a  ship  through  the  water  with  great  power,  and 
we  wish  to  investigate  it  philosophically,  the  first  question 
to  be  asked  is, Where  does  the  force  come  from?  and  in  the 
same  manner,  when  we  see  a  force  disappearing,  as,  for  in- 
stance, when  an  express  train  that  has  been  moving  with 
great  impetuosity  is  gradually  brought  to  a  stand,  or  a 
bullet  in  rapid  flight  through  the  air  is  stopped  by  a  wall, 
we  have  to  inquire,  Where  has  the  force  gone  to  ?  The  idea 
that  either,  in  the  one  case,  it  has  been  created  or  called 
into  existence  by  any  kind  of  contrivance  or  mechanism, 
or,  in  the  other,  that  any  portion  of  it,  however  small,  can 
have  come  to  an  end,  or  ceased  to  exist,  is  wholly  inad- 
missible ;  and  this  principle  of  the  absolute  continuity 
and  persistence  of  all  the  force  which  is  in  action  in  the 
visible  universe  around  us  lies  at  the  foundation  of  all  real 
knowledge  on  the  subject." 

We  have  an  excellent  illustration  of  this  principle,  in 
one  of  its  forms,  in  the  rotation  of  the  grindstone,  as  im- 


30 


CEANK    MOTION. 


pelled  by  the  efforts  of  Rick,  which  produced  in  the  end 
such  a  violent  result.  The  great  force  of  rotation  which 
the  stone  acquired  consisted  only  of  an  accumulation  of  a 
great  many  small  forces  imparted  to  it  by  the  pressure  of 
Rick's  foot  upon  the  pedal,  as  may  be  seen  in  the  action  of 
a  common  grindstone  in  any  farmer's  yard. 


SANK  MOTION. 


The  grindstone,  turning  in  the  direction  denoted  by  the 
arrow,  whenever,  at  each  rotation,  it  comes  into  the  posi- 
tion represented  in  the  engraving,  the  boy,  bearing  with 
his  whole  weight  upon  the  end  of  the  treadle,  transfers  all 
the  force  represented  by  the  descent  of  that  weight  to  the 
crank,  and  so  to  the  stone.  Of  course,  when  the  crank 
comes  down  to  the  lowest  point,  and  then  turns  to  go  up 
on  the  other  farther  side,  the  boy  raises  his  foot,  and  then, 
as  soon  as  it  passes  over  the  highest  point,  and  turns  to 
come  down  on  the  hither  side,  he  bears  on  again  with  all 


EXACT   CALCULATIONS.  31 

his  force,  and  so  adds  another  impulse  to  the  motion  of  the 
stone ;  that  is,  he  sends  in,  as  it  were,  an  additional  force 
to  be  added  to  what  lie  had  imparted  before.  Thus  he 
goes  on  sending  in  an  addition  to  the  force  previously 
communicated  to  the  stone,  at  every  rotation  of  it,  until 
the  quantity  accumulated  becomes  very  large. 

The  reader  who  likes  to  have  precise  ideas  on  any  sub- 
ject of  this  kind  will  perhaps  be  interested  in  seeing  how 
exact  calculations  are  made  in  such  cases  as  this,  and  how 
quantities  of  force  can  be  measured  and  expressed  numer- 
ically. Let  us  suppose,  then,  that  Rick  weighed  ninety 
pounds,  and  that  at  the  right  moment  of  each  revolution 
he  bore  with  his  whole  weight  on  the  pedal.  Let  us  also 
suppose  that  the  end  of  the  treadle-bar  on  which  his  foot 
rested  descended  at  the  rate  of  six  inches  in  a  second. 
Then  the  force  that  he  imparted  would  be  that  of  ninety 
pounds  moving  at  the  rate  of  six  inches  a  second.  Now 
let  us  suppose  that  the  stone  weighed  six  times  as  much  as 
Rick's  body ;  then  the  force  which  Rick  imparted  to  it 
would  be  a  motion  one  sixth  as  great — that  is,  the  motion 
of  one  inch  a  second. 

This  means,  of  course,  an  average  motion  of  all  the  parts 
of  the  stone.  The  parts  near  the  circumference  would  evi- 
dently move  much  more  rapidly  than  the  parts  near  the  cen- 
tre. Then,  again,  some  portion  of  the  force  which  Rick's 
weight  would  exert  would  be  expended  in  overcoming  the 
friction,  and  there  would  be  many  other  considerations 
connected  with  the  manner  in  which  the  pitman — that  is, 
the  connecting  rod  between  the  crank  and  the  middle  of 
the  treadle-bar* — acts  in  the  different  parts  of  its  course ; 
but  the  general  principle  is  simple  and  plain,  as  Lawrence 

*  A  connecting  bar  of  this  kind  in  machinery,  which  acts  in  communi- 
cating force  hy  a  reciprocating  motion  up  and  down,  is  called  a  pitman, 
from  the  analogy  of  its  action  to  that  which  the  man  who  stands  in  the 


32  CKANK   MOTIOX. 

presented  it  to  the  boys,  namely,  that  the  whole  of  the 
very  considerable  force  with  which  the  stone  revolved  at 
last  was  made  up  by  the  accumulation  of  comparatively 
small  forces  which  Rick  impressed  upon  it  through  the 
treadle  as  the  crank  went  round;  and  that  the  whole  amount 
of  the  greater  force,  together  with  the  small  portion  which 
had  been  deflected  through  friction,  was  neither  more  nor 
less  than  exactly  equal  to  the  sum  of  all  the  smaller  ones. 

A  heavy  wheel  like  this  grindstone,  moving  with  a  force 
made  up  of  the  sum  of  a  great  many  smaller  ones,  is  not 
only  an  accumulator  of  force,  but  it  acts  also  as  an  equalizer 
of  its  flow.  The  force  imparted  to  it  is  intermittent;  that 
is,  it  consists  of  a  succession  of  impulses ;  but  the  force 
with  which  the  stone  revolves  is  steady  and  uniform.  This 
is  of  great  importance  in  the  case  ^of  the  grindstone,  be- 
cause it  is  necessary,  in  grinding,  that  the  tool  should  be 
held  upon  the  stone  with  a  uniform  and  steady  pressure ; 
and  if  the  stone  were  not  heavy — that  is,  if  it  did  not  con- 
tain a  large  quantity  of  matter,  to  continue  steadily  in  mo- 
tion when  motion  was  once  imparted  to  it — it  would  be 
stopped  by  the  friction  of  the  tool  when  the  crank  had 
passed  the  lowest  point  at  each  revolution,  and  was  as- 
cending on  the  farther  side,  during  which  part  of  its  revo- 
lution no  additional  force  could  be  imparted  to  it. 

All  machinery  which  is  moved  by  a  succession  of  im- 
pulses such  as  those  given  by  means  of  a  crank  must  have 
some  heavy  wheel  to  receive  and  store,  and  thus  equalize 
the  force.  When  the  machinery  itself  consists  of  heavy 
wheels,  they  serve  this  purpose  themselves  ;  but  when  the 
machinery  is  light,  as  in  the  case  of  a  sewing-machine,  a 
heavy  wheel  must  be  expressly  provided  to  accomplish  this 
end.  Such  a  wheel  is  called  a  fly-wheel,  and  is  usually 

pit,  in  sawing,  exerts  in  pushing  up  and  pulling  down  the  saw,  by  means  of 
the  handles  on  the  lower  end  of  it. 


UNIVERSAL    PRINCIPLE.  33 

made  of  iron,  with  the  greatest  portion  of  the  weight  in 
the  rim,  where  the  motion  is  swiftest,  and  where,  of  course, 
the  greatest  quantity  of  force  can  be  stored.  Such  a  wheel 
may  be  seen  connected  with  the  treadle  beneath  the  table 
in  any  sewing-machine.  In  some  cases  these  fly-wheels 
are  of  immense  size,  and  are  generally  used  as  above  ex- 
plained in  receiving  and  storing  large  quantities  of  force 
received  in  intermitted  impulses  — which  is  always  the 
character  of  the  force  transmitted  by  a  crank — and  deliv- 
ering it  afterward  to  other  parts  of  the  machinery  in  a 
continued  and  equable  flow. 

The  principle  which  was  thus  illustrated  by  the  case  of 
the  grindstone,  that  whenever  we  see  force  of  any  kind  or 
in  any  quantity  in  action,  we  may  be  sure  that  it  proceeds 
from  some  other  force  previously  existing  in  the  same  or 
in  some  other  form,  and  precisely  equal  to  it  in  amount, 
and  that  when  it  ceases  to  act  it  is  not  annihilated — that 
is,  it  does  not  cease  to  exist,  but  passes  oiF  into  some  other 
body  in  the  same  or  in  some  other  form,  but  without  at  all 
changing  its  amount,  is  universally  true.  The  case  of  the 
grindstone  does  not,  indeed,  prove  this  principle.  It  is  only 
one  illustration  of  it.  The  case  of  the  grindstone,  more- 
over, only  shows  the  operation  of  it  in  respect  to  the  equal- 
ity between  impulses  of  force  communicated  by  Rick's 
foot,  and  the  revolving  force  of  the  stone  made  up  by  the 
accumulation  of  these  impulses.  Lawrence  did  not  show 
where  and  in  what  form  the  force  existed  before  it  ap- 
peared in  the  boy's  foot,  or  where  it  went  in  its  disappear- 
ing, as  the  grindstone  gradually  came  to  a  state  of  rest. 
These  points  he  reserved  to  be  considered  and  explained 
another  time.  The  principle  itself  has,  however,  been  fully 
proved  to  be  universally  true,  so  fully  that  there  is  no 
longer  any  doubt  of  it  in  the  minds  of  any  scientific  or 
even  well-informed  man. 

B2 


34  CKANK    MOTION. 

It  would  have  been  well  for  mankind  if  this  great  truth 
could  have  been  earlier  and  more  generally  understood,  for 
it  would  have  saved  many,  many  years  of  valuable  time 
spent,  and  vast  sums  of  money  that  have  been  wasted,  in 
attempting  to  conti'ive  means  for  the  production  of  force, 
under  the  name  of  machines  of  perpetual  motion.  The 
phrase  perpetual  motion  is  an  unfortunate  one,  in  a  philo- 
sophical point  of  view,  inasmuch  as  we  have  perpetual  mo- 
tion already  all  around  us,  every  where,  instead  of  its  being 
any  thing  new  yet  to  be  discovered.  The  particles  of  all 
bodies  that  we  know  are  in  a  state  of  incessant  movement. 
The  earth  itself  is  in  rapid  rotation  around  the  sun,  and 
the  most  solid  rocks  are  constantly  undergoing  internal 
changes  produced  by  expansions,  and  contractions,  and  oth- 
er movements  of  the  particles  among  themselves.  Thus, 
instead  of  there  being  any  difficulty  in  producing  perpetual 
motion,  it  is  impossible  to  escape  from  it.  We  can  not  by 
any  conceivable  means  produce  in  any  substance  a  condi- 
tion of  absolute  rest. 

The  real  object  of  the  so-called  perpetual-motion  ma- 
chines is  the  creation  of  force,  or  the  expanding  of  a  single 
small  force  into  a  great  one  by  means  of  some  ingenious 
combination  of  levers  and  wheels,  or  other  machinery — 
effects  which,  by  the  very  constitution  of  nature,  can  not 
possibly  be  produced.  In  all  cases  where  a  new  machine 
is  proposed  for  doing  work,  the  first  question  to  be  asked 
in  respect  to  it  is,  from  what  source  is  the  force  derived  by 
which  the  machinery  is  driven  ?  If  any  adequate  source 
offeree  is  pointed  out,  the  machine  may  be  a  success.  This 
source  of  force  may  be  in  the  movement  of  the  wind,  the 
falling  or  running  of  water,  the  rising  or  falling  of  the  tide, 
the  combustion  of  wood  or  coal,  as  in  a  steam-engine,  or 
that  of  zinc,  as  in  an  electro-magnetic  engine.  There  must 
be  a  source  offeree  somewhere,  external,  in  its  nature,  to 


FUNDAMENTAL    LAW.  35 

the  machine  which  it  sets  in  motion ;  for  no  machinery  can 
by  any  possibility  create  or  produce  its  own  force,  or  in- 
crease in  the  least  degree  the  amount  which  is  furnished 
by  the  source,  whatever  it  is,  from  which  it  draws  its  sup- 

pty- 

Let  every  reader  of  this  book,  therefore,  understand  and 
fix  indelibly  this  fundamental  principle,  namely, 

All  force,  as  it  exists  in  nature  or  in  human  contrivances, 
exists  in  fixed  'and  definite  quantities,  which  can  not  be  in- 
creased in  any  other  way  than  by  accumulating  many  small 
forces  to  form  a  great  one,  or  diminished  in  any  other  way 
than  by  being  divided  and  dispersed. 


MECHANICAL   FOKCE. 


CHAPTER  III. 

MECHANICAL   FOKCE. 

IN  the  case  described  in  the  last  chapter,  the  function  of 
the  grindstone,  in  respect  to  its  action  as  a  fly-wheel,  was 
this,  namely,  to  receive  the  force  in  the  form  of  a  succession 
of  impulses  imparted  by  the  weight  of  Rick  at  each  revolu- 
tion of  the  crank,  and  then  to  deliver  it,  at  the  surface  of 
the  stone,  in  an  equable  and  continuous  flow.  In  some 
cases,  however,  the  action  of  a  fly-wheel  is  the  reverse  of 
this.  It  receives  the  motion  in  a  continuous  flow  from  the 
machinery  by  which  it  is  driven,  and  delivers  in  a  succes- 
sion of  impulses,  when  such  impulses — that  is  to  say,  inter- 
mittent exertions  of  force — are  required  by  the  nature  of 
the  woi-k  to  be  done. 

Such  intermittent 
action,  for  example, 
is  required  in  the 
case  of  such  an  en- 
gine, as  is  shown  in 
the  accompanying 
engraving,  for  cut- 
ting off  heavy  iron 
bars  into  portions 
of  a  given  length. 

It  seems  wonder- 
ful that  bars  of  such 
thickness  can  be  cut 
offin  this  manner  at 


IKON  till  K  A  US. 


PONDEROUS   SHEARS.  37 

a  single  stroke  by  a  pair  of  shears.  But  there  is  no  diffi- 
culty in  doing  it,  and  that,  too,  with  great  rapidity,  pro- 
vided that  a  sufficient  force  to  overcome  the  cohesive 
strength  of  such  a  mass  of  iron  is  accumulated  in  the  im- 
mense fly-wheel,  which  always  forms  a  part  of  such  ma- 
chinery, and  is  brought  to  the  work  by  a  band  or  some 
other  connection,  and  that  the  jaws  of  the  shears  are  made 
massive  and  solid  enough  to  hold  the  force  and  deliver  it 
all  at  the  precise  point  or  line  in  the  iron  bar  where  it  is 
required.  The  iron  is  cut  off  in  such  a  case  as  if  the  bar 
was  one  of  wax.  The  portions  are  made  equal  by  means 
of  the  gauge  seen  toward  the  right,  against  which  the  work- 
man, after  each  portion  is  cut  off,  pushes  the  bar,  and  thus 
measures  another  portion  to  be  cut  off  at  the  next  descent 
of  the  cutter.  The  portions  thus  cut — forming  short  bars 
— fall  in  a  heap  upon  the  floor  below. 

In  this  case  it  is  evident  that  the  steady  and  equable 
force  involved  in  the  motion  of  the  ponderous  fly-wheel,  or 
in  that  of  other  portions  of  the  machinery  not  seen  in  the 
engraving,  is  delivered,  not  equally  and  steadily  in  doing 
its  work,  but  in  a  series  of  prodigious  though  momentary 
impulses,  each  one  taking  effect  during  the  instant  that 
the  jaw  of  the  shears  is  coming  down  to  cut  off  the  bar. 
Dnring  the  time  while  the  jaw  is  rising  again,  and  the  work- 
man is  pushing  the  bar  forward  into  the  right  position  for 
a  new  cut,  there  is,  of  course,  an  intermission  in  the  expend- 
iture of  force,  for  it  is  plain  that  comparatively  very  little 
force  is  required  for  raising  the  jaw  to  its  former  position 
in  order  to  bring  it  into  readiness  for  a  second  stroke. 

Thus  it  is  plain  that  in  such  a  case  as  this  the  force  that 
is  stored  in  the  fly-wheel  of  the  machinery  is  delivered,  not 
in  a  continuous  flow,  but  in  a  succession  of  very  powerful 
impulses. 

A  curious  example  of  the  different  modes  of  the  trans- 


38  MECHANICAL    FORCE. 

mission  of  force  is  given  in  the  accompanying  engraving, 
from  a  drawing  made  by  a  French  traveler  of  a  primitive 
species  of  lathe  which  he  observed  in  use  among  the  na- 
tives of  Algeria,  in  Africa. 

The  cord,  it  will  be  observed,  on  which  the  man  bears 
his  foot,  is  passed  once  around  the  spindle  which  forms  the 
axis  on  which  the  work  is  fixed,  and  the  farther  end  of  it 
is  attached  to  the  end  of  an  elastic  wooden  spring.  By 
this  arrangement,  of  course,  in  bearing  upon  the  cord  with 
his  foot,  the  workman  causes  the  axis,  with  the  work  upon 
it,  to  revolve,  and  the  top  of  the  elastic  rod  to  bend  toward 
him.  Thus  a  portion  of  the  force  which  he  impresses  upon 
the  cord  is  conveyed  to  the  axis  and  to  the  work,  and  an- 
other portion  is  expended  in  bending  the  spring,  thus  stor- 
ing itself,  as  it  were,  in  the  elasticity  of  the  wood.  When 
the  workman  raises  his  foot,  this  stored  force  comes  into 
action  to  turn  the  axis  and  the  work  upon  it  back  to  its 
former  position.  Thus  the  man  turns  the  axis  and  the 
work  back  and  forth  by  an  alternating  motion,  turning  it 
forward  by  the  direct  action  of  his  foot,  and  back  again  by 
the  force  imparted  to  the  wooden  spring,  and  stored  in  it 
till  it  comes  into  action  again  when  the  pressure  of  the  foot 
is  relieved. 

In  precisely  what  condition  a  force  can  be  stored  in  this 
manner  in  the  elasticity  of  a  substance,  so  to  speak,  we 
shall  see  hereafter,  so  far,  at  least,  as  in  the  present  state 
of  our  knowledge  on  the  subject  it  can  be  explained. 

Although  this  engraving  answers  very  well  as  an  illus- 
tration of  the  points  above  referred  to,  it  still  represents  a 
very  awkward  arrangement  for  any  practical  purposes  of 
turning  except  the  shaping  of  pottery,  as  there  is  no  con- 
venient mode  shown  for  supporting  the  tool,  though  the 
long  bar  seen  between  the  workman  and  the  work  would 
serve  this  purpose  for  a  certain  part  of  the  operation.  The 


THE    BOW-LATHE.  41 

tool,  in  almost  all  cases  in  turning,  requires  a  fixed  and 
very  firm  support. 

Lathes  for  practical  purposes  are,  however,  not  unfre- 
quently  made  on  a  principle  substantially  the  same  as  is 
illustrated  in  this  example,  by  farmers'  boys  and  other  per- 
sons who  do  not  wish  to  incur  much  expense  in  their  work. 
The  spring,  however,  in  these  cases,  instead  of  being  set  up 
perpendicularly  in  the  floor,  is  placed  horizontally  above, 
over  the  bench,  the  fixed  end  of  it  being  fastened  to  the 
beams  or  rafters,  and  the  free  end  extending  over  the  work. 
The  work  is  held  between  two  pivots  set  in  blocks,  Avhich 
blocks  are  set  firmly  in  the  bench.  The  cord  from  the  free 
end  of  the  spring  is  brought  down,  and,  after  being  carried 
once  round  a  part  of  the  wood  to  be  turned — in  a  little 
groove  made  for  it — passes  down  through  an  opening  in 
the  bench  made  for  the  purpose  to  a  treadle,  constructed 
somewhat  like  the  treadle  of  the  grindstone,  below,  near  the 
floor.  Of  course,  the  workman  can  cause  the  work  to  re- 
volve three  or  four  times  in  the  direction  required  for  his 
tool  by  bearing  down  upon  the  treadle,  and  then,  on  rais- 
ing his  foot,  the  spring  draws  the  treadle  up  again,  carry- 
ing the  work  round  by  a  backward  motion  into  its  original 
position.  There  is  a  bar  of  hard  wood,  which  passes  across 
from  one  of  the  blocks  to  the  other,  to  serve  as  a  rest  for 
the  tool  in  turning.  Such  a  lathe  as  this  is  called  a  spring 
lathe. 

This  kind  of  lathe,  though  comparatively  easy  to  make, 
is  not  very  convenient,  or,  rather,  efficient  for  work  ;  for,  as 
the  wood  to  be  turned  does  not  revolve  continuously  in 
the  same  direction,  but  turns  and  returns  by  a  series  of  al- 
ternating movements,  the  tool  must  only  be  held  up  to  the 
work  while  it  is  moving  in  the  right  direction.  Of  course, 
it  is  only  half  of  the  time  that  the  tool  is  producing  any 
useful  effect.  Then,  moreover,  as  there  is  no  flv-wheel  to 


42  MECHANICAL   FOECE. 

steady  and  equalize  the  motion,  the  action  is  not  so  satis- 
factory in  any  respect. 

For  such  a  lathe  as  this,  some  building  which  can  be 
used  as  a  shop  is  required,  and  a  considerable  degree  of 
strength,  and  some  experience  and  skill  in  doing  such  work, 
is  necessary  for  the  construction  of  it.  There  is  another 
kind,  however,  in  which  the  force  is  transmitted  in  a  some- 
what analogous  manner,  that  any  ingenious  boy  can  make, 
and  which  can  be  used  on  any  table  by  the  fireside. 


THE   BOW-LATHE. 


It  is  called  the  bow-lathe,  because  it  is  worked  by  means 
of  a  bow  held  in  one  hand  by  the  workman,  while  he  man- 
ages the  tool  with  the  other.  It  consists,  in  its  simplest 
form,  of  a  board  of  any  convenient  size — as,  for  example, 
a  foot  long  and  six  or  eight  inches  wTide — with  two  stand- 
ards near  the  two  ends,  as  shown  in  the  engraving.  There 
is  a  bar  extending  horizontally  from  one  of  these  standards 
to  the  other,  at  the  proper  height,  for  a  "  rest"  to  support 
the  tool,  l^ear  the  top  of  each  standard  is  inserted  a  screw. 
The  inner  ends  of  both  of  these  screws  are  carefully  formed 
into  smooth  tapering  points,  to  enter  into  the  ends  of  the 


HOW   TO   MAKE    A   BOW-LATHE.  43 

piece  of  wood  to  be  turned.  Common  "  wood  screws,"*  as 
they  are  called,  will  answer  this  purpose  very  well,  but  they 
should  be  of  good  size,  and  the  ends  should  be  prepared  by 
filing  off  the  threads  for  half  an  inch,  and  carefully  form- 
ing a  conical  point  at  the  end  of  each.  These  ends  should 
be  ground  smooth,  and  then  polished  upon  a  whetstone,  so 
as  to  prevent  their  wearing  the  wood.  The  tips  should 
also  be  oiled  a  little  when  in  use.  The  screw  at  one  end, 
besides  passing  through  the  top  of  the  stand,  should  also 
have  a  small  block  like  a  nut  on  the  outside,  as  shown  in 
the  engraving,  by  means  of  which  it  can  be  held  tight  in 
its  place  while  the  work  is  going  on. 

Any  boy  with  ingenuity  and  skill  enough  to  make  a  bow 
and  arrow  can  make  such  a  bow  as  is  required  for  a  lathe 
of  this  kind  by  taking  the  one  represented  in  the  engrav- 
ing as  his  guide  as  to  the  form.  The  string  should  be  a 
very  close  and  compact  one ;  cat-gut  is  best. 

The  wood  to  be  turned  must  be  made  of  the  right  length, 
and  then  shaped  roughly  to  the  size  and  form  required. 
Small  holes  must  be  made  in  each  end  to  receive  the  piv- 
ots, and  a  quai'ter  of  a  drop  of  oil  put  in  each.  The  cord 
of  the  bow  is  to  be  wound  once  round  the  wood,  and  then, 
one  end  being  fitted  to  the  left-hand  pivot,  the  right-hand 
screw  is  to  be  turned  forward  till  the  point  enters  the  hole 
in  the  other  end,  so  as  to  hold  the  wood  in  its  place,  and 
the  binding  nut  at  the  end  is  to  be  tightened.  The  boy 
then,  holding  the  bow  in  his  left  hand,  and  the  tool — which 
must  be  at  first  of  the  gouge  form — in  his  right,  begins  his 
work. 

The  first  thing  to  be  done  with  the  tool  is  to  form  a 
groove  near  the  left-hand  end  of  the  piece  of  wood  for  the 
cord  or  bow-string  to  run  in.  In  the  engraving  the  bow- 

*  So  called  because,  though  made  of  iron,  they  are  intended  to  be  used 
in  wood. 


44  MECHANICAL   FORCE. 

string  is  represented  as  encircling  the  wood  in  the  groove ; 
but  the  place  which  it  must  occupy  while  the  workman  is 
cutting  the  groove — which  must  be  done  by  holding  the 
tool  in  the  left  hand — is  a  little  to  the  right  of  it.  The 
drawing  is  made  in  this  way  the  better  to  show  the  ulti- 
mate form  and  position  of  the  groove.  Of  course,  when 
the  groove  is  finished,  the  bow-string  must  be  run  along  to 
the  left,  into  it,  and  then  the  work,  with  the  gouge  to  the 
right,  can  go  on  regularly. 

If  the  young  workman  finds  that  lie  can  not  manage  the 
tool  with  the  left  hand  very  well  in  making  the  groove,  he 
can,  if  he  chooses,  turn  the  piece  of  wood  end  for  end  be- 
tween the  pivots,  and  so  form  the  groove  in  what  will  be 
the  right-hand  end  of  it,  and  then  reverse  it  again  when 
the  groove  is  made. 

However  this  may  be,  any  boy,  however  ingenious,  may 
depend  upon  finding  this  work  for  a  time  full  of  vexation 
and  discouragement;  for  the  great  difficulty  in  the  case 
of  such  a  lathe  as  this  is,  not  to  make,  it,  but  to  acquire  the 
skill  to  use  it.  It  is  difficult,  in  the  first  place,  to  attach 
the  bow  to  the  piece  of  wood  to  be  turned,  with  the  cord 
wound  once  around  it  iu  such  a  manner  as  to  bring  the 
bow  on  the  upper  side  of  it ;  though,  after  one  learns  to  do 
this,  nothing  is  more  easy.  Then  it  is  difficult  for  a  young 
workman  to  acquire  the  knack  of  moving  the  bow  with  one 
hand  and  holding  the  tool  with  the  other,  and  of  pressing 
the  edge  of  the  tool  up  to  the  work  only  while  pulling  the 
bow  toward  him,  for  it  is  only  then  that  the  wood  is  re- 
volving in  the  right  direction.  Then,  after  learning  to 
work  successfully  with  a  gouge-shaped  tool,  it  is  very  dif- 
ficult to  learn  the  art  of  smoothing  the  work  with  a  chisel, 
for  it  is  almost  impossible  for  a  beginner  to  prevent  the 
corners  of  the  chisel  from  catching  in  the  wood. 

Any  intelligent  boy,  however,  who  has  ingenuity,  pa- 


JEWELERS'  LATHES.  45 

tience,  and  perseverance  enough  to  surmount  all  these  dif- 
ficulties, will  be  able  to  amuse  himself  a  great  deal  with 
such  a  contrivance  as  this,  and  when  he  learns  to  manage 
it  right,  can  turn  small  ninepins,  and  tops,  and  checker- 
men,  and  tool-handles,  and  other  such  things  with  it,  and 
in  so  doing  will  learn  practically  a  great  deal  about  force, 
and  the  art  of  dealing  with  it,  and  the  action  of  it  upon 
different  kinds  of  materials,  and  will  acquire  much  other 
knowledge  which  will  be  of  great  use  to  him  in  helping 
him  to  understand  machinery,  and  lead  him  to  take  an  in- 
terest in  it  as  long  as  he  lives. 

In  fact,  lathes  constructed  on  precisely  this  principle,  but 
made  neatly  of  iron  and  brass,  are  in  constant  use  by  me- 
chanics for  light  turning,  as  any  one  can  see  by  inquiring 
at  any  jeweler's  or  watchmaker's,  and  watching  one  while 
it  is  in  operation. 

The  watchmakers  turn  arbors,  and  wheels,  and  screws, 
and  other  small  work,  sometimes  of  brass,  and  sometimes 
of  softened  steel,  in  such  lathes.  They  secure  the  lathe 
itself  firmly,  while  they  are  using  it,  by  holding  it  in  a  vice 
which  is  secured  to  their  bench.  A  wooden  lathe  of  this 
kind,  to  be  used  upon  a  table,  may  either  be  made  upon  a 
plank  base  heavy  enough  to  keep  it  steady,  or,  if  the  base- 
board is  thin,  it  may  be  held  to  the  table  by  clamps  made 
of  blocks  of  wood  of  the  right  size,  with  square  notches  cut 
in  them,  tightened  by  wedges  crowded  in  either  between 
the  upper  side  of  the  notch  in  the  clamp  and  the  base-board 
above,  or  between  the  under  side  and  the  lower  edge  of 
the  table  below. 

But  to  return  to  our  story.  Lawrence  explained  to  John 
and  to  Rick  some  of  the  principles  here  referred  to  in  re- 
spect to  the  management  of  that  form  of  force  which  con- 
sists in  mechanical  motion,  in  the  course  of  conversation 
with  them  at  the  grindstone  and  at  the  lathe.  After  hav- 


46  MECHANIC  AT,    FORCE. 

ing  remedied  the  damage  done  to  the  treadle  of  the  grind- 
stone, he  went  to  the  lathe,  asking  Rick,  by  the  Avay,  what 
was  the  best  kind  of  wood  for  him  to  take  to  make  the 
bat  of. 

"  The  very  hardest  and  toughest  kind  of  wood  that  you 
can  get,"  said  Rick.  "  You  see  the  balls  are  very  hard,  and 
we  strike  with  all  our  might,  and  the  bats,  no  matter  how 
hard  the  wood  is,  soon  get  broken  or  battered  to  pieces." 

"Yes,"  said  Lawrence.  "You  draw  the  bat  back  as  far 
as  you  can,  and  then  you  concentrate  in  it  all  the  force  you 
can  impart  to  it  from  your  arms  through  the  whole  length 
of  the  swing  of  them,  and  deliver  the  whole  in  a  single  in- 
stant into  the  ball." 

"And  send  it  spinning,"  said  Rick. 

Lawrence  asked  how  ash  would  do ;  but  Rick  said  that 
ash  would  not  do  at  all.  "It  is  tough  and  springy,  and 
good  enough  for  some  things,"  he  added, "but  it  soon  splits 
into  shivers  if  we  use  it  for  a  bat." 

Lawrence  finally  made  choice  of  a  piece  of  seasoned  ma- 
ple, and  fixed  it  in  the  lathe.  He  asked  Rick  various  ques- 
tions about  the  length  and  the  other  dimensions  best  for  a 
bat,  and  followed  his  directions  exactly  in  marking  out  the 
work.  Then,  when  he  was  ready  to  begin,  he  took  a  gouge, 
and  asked  Rick  if  he  would  work  the  treadle  for  him  Avhilc 
he  turned. 

"Oh  yes,"  said  Rick;  "I  can  do  that  well  enough." 

Rick  began,  and,  to  show  how  well  he  could  do  it,  he  was 
soon  driving  the  machinery  so  furiously  that  Lawrence  was 
obliged  to  check  him,  telling  him  that  a  moderate  and 
steady  motion  was  Avhat  was  required. 

Rick  watched  the  effect  of  the  gouge  upon  the  rapidly 
revolving  wood,  and  soon  began  to  be  greatly  interested 
in  the  operation.  At  last  Lawrence  put  the  gouge  into  his 
hands,  and  asked  him  to  sec  if  he  could  not  work  the  treadle 


KH'K     AT    WO  UK. 


47 


ai:d  manage  the  cutting  too.  Rick  seemed  at  first  to  hesi- 
tate, but  he  soon  became  willing  to  make  the  attempt, 
Lawrence  standing  by  and  watching  the  operation.  John 
*-as  then  in  another  part  of  the  shop. 


KICK  AT  TUB   LATHE. 


John  had  listened  to  Lawrence's  explanations,  and  to  his 


48  MECHANICAL    FOKCE. 

account  of  the  bow-lathe,  with  much  interest,  and,  although 
he  had  the  use  of  Lawrence's  lathe,  which  was,  of  course, 
much  more  convenient  for  actual  use,  he  determined  that 
he  would  make  a  bow-lathe  for  himself  some  time,  "just 
for  fun,"  as  he  said.  Lawrence  proposed  to  Rick  that  lie 
should  make  one  too,  promising  to  help  him  in  doing  it. 
But  Kick  replied  somewhat  churlishly  that  he  did  not  want 
such  a  thing.  He  did  not  think  that  it  would  do  him  any 
good. 

However,  when  he  came  to  the  trial  of  the  gouge  in  Law- 
rence's lathe,  and  found  how  easily  and  how  well  he  suc- 
ceeded in  bringing  the  rough  piece  of  wood  into  an  approx- 
imation to  its  true  form  for  a  bat,  he  became  for  a  few  min- 
utes somewhat  interested  in  the  operation,  though  it  is 
probable  that  this  interest  depended  altogether,  or  almost 
altogether,  upon  the  fact  that  it  was  a  bat  that  he  was  mak- 
ing, and  extended  very  little  to  the  scientific  considerations 
in  respect  to  the  nature  of  force  which  were  involved  in 
the  process  of  turning. 

After  the  bat  had  been  brought  substantially  into  its 
proper  form  by  the  gouge,  Lawrence  finished  it  with  the 
chisel,  and  smoothed  and  polished  it  with  sand-paper,  while 
Rick  worked  the  treadle,  driving  the  machinery — as  it  was 
proper  to  do  in  the  process  of  polishing — at  great  speed. 
When  it  was  finished,  Lawrence  took  it  out  of  the  lathe 
and  handed  it  to  Rick. 

"  Now  let  us  go  out  and  try  it,  and,  if  you  like  it,  you  can 
have  it.  Or  can  you  tell  by  handling  it  how  it  will  work?" 

"I  can  tell  pretty  well  by  the  feeling  of  it,"  said  Rick, 
taking  hold  of  it  with  his  two  hands,  and  holding  it  out  as 
if  about  to  strike  a  ball  with  it. 

"  Yes,"  said  he,  "  that  will  do  pretty  well.  But  I  have 
got  a  ball  in  my  pocket,  and  we  will  go  out  and  try  it. 
But  do  you  say  I  may  have  it  for  my  own?" 


RESULT   OF   TUB    FIRST   EXPERIMENT.  49 

"Yes,"  replied  Lawrence.  "Only  you  must  come  back 
in  a  few  days  after  you  have  tried  it  on  the  play-ground, 
and  tell  me  how  it  works." 

So  they  went  out  upon  the  grass-ground  behind  the  shop 
to  try  the  bat.  John  remained  in  the  doorway  looking 
on.  Rick  took  a  ball  out  of  his  pocket,  and  tossing  it  a 
foot  or  two  in  the  air,  and  bringing  the  bat  into  position 
in  a  moment  so  as  to  intercept  it  as  it  fell,  he  struck  it  fair 
and  square,  with  tremendous  force,  at  precisely  the  right 
instant  of  its  descent.  The  ball  soared  to  a  great  height. 
Rick  followed  it  with  his  eyes,  and  then  began  to  walk 
along  rapidly  in  the  direction  it  was  going.  He  caught  it 
as  it  came  down,  put  it  in  his  pocket,  and  walked  off  in  the 
direction  toward  home  without  looking  around  at  all  to 
Lawrence  and  John,  and  without  any  word,  either  of  thanks 
or  of  parting,  at  leaving  them. 

Lawrence  turned  toward  the  door  where  John  was  stand- 
ing, and  advanced  with  a  very  curiously  expressive  smile 
upon  his  countenance.  John  was  writhing  to  and  fro  in 
convulsions  of  laughter,  now  stooping  down  with  his  hands 
upon  his  knees,  and  now  holding  his  sides  in  desperate  ef- 
forts to  restrain  himself  within  such  bounds  that  Rick 
should  not  hear  him. 

"A  perfect  failure !"  he  said,  as  soon  as  he  recovered  suf- 
ficient composure  to  speak  articulately.  "  I  told  you  you 
could  not  interest  him  in  any  thing  beyond  ball-playing." 

"  Perfect  success  !"  rejoined  Lawrence.  "  I  am  entirely 
satisfied  with  the  result  of  my  first  experiment." 

And  so  they  went  back  into  the  shop. 
C 


50     TRANSFER  OF  FORCE  BY  PULLEYS  AND  BANDS. 


CHAPTER  IV. 

TRANSFER   OF   FORCE   BY   PULLEYS   AND   BANDS. 

THE  word  force,  in  common  parlance,  is  used  in  a  great 
many  different  senses,  some  of  which  are  quite  vague  and 
indeterminate.  As  used  by  Lawrence  in  his  conversation 
about  wheels  and  machinery  with  John  and  Rick,  as  nar- 
rated in  the  last  chapter,  it  relates  solely  to  what  is  some- 
times designated  as  mechanical  force — that  is,  the  visible 
motion  of  masses  of  matter.  There  are  various  other 
forms  of  force,  which  consist,  as  will  hereafter  be  shown,  of 
changes  taking  place,  or  of  effects  produced,  in  the  inter- 
nal constitution  of  substances.  These  will  be  considered 
hereafter.  We  are  now  dealing  only  with  mechanical  force, 
or  energy,  which  is  compounded  in  respect  to  its  quantity, 
and  with  reference  to  a  certain  important  class  of  effects 
produced  by  it  of  the  quantity  of  matter  that  is  in  motion, 
and  the  velocity  with  which  it  moves. 

But  this  kind  of  mechanical  force,  it  is  evident,  may  ex- 
ist in  a  great  variety  of  forms,  or  rather,  perhaps,  condi- 
tions. It  may  be  rectilinear  and  continuous,  as  in  a  block 
sliding  upon  ice ;  it  may  be  rectilinear  and  reciprocating, 
as,  for  instance,  in  the  case  of  the  piston  of  a  steam-engine, 
which  moves  to  and  fro,  or  up  and  down,  in  successive  al- 
ternations ;  it  may  be  uniformly  accelerated,  as  when  a 
grindstone  is  made  to  go  faster  and  faster  by  uniform  ad- 
ditions to  its  velocity  every  instant,  or  when  a  weight  let 
fall  from  a  height  descends  with  steadily  increasing  veloc- 
ity to  the  ground ;  and  it  may  be  intermittent — that  is,  it 
may  advance  by  a  series  of  distinct  impulses,  with  inter- 


MECHANICAL   COMBINATIONS.  51 

vals  of  rest  between  them.  And  so  it  may  be  rotary  con* 
tinuous  or  rotary  intermittent.  In  a  word,  the  number 
and  variety  of  kinds  of  motion  which  may  be  required  in 
working  of  machinery  is  without  end ;  while  all  of  them 
must  be  derived  from  one  common  source — whatever  that 
source  may  be — whether  the  up  and  down  motion  of  the 
piston  in  the  steam-engine,  or  the  slow  revolving  of  the 
great  water-wheel  in  the  mill. 

Now  nothing  is  more  common  than  the  number  and  va- 
riety of  the  contrivances  by  which  mechanical  force  is 
transmitted,  and  modified  in  transmission,  in  the  construc- 
tion of  machinery.  Of  course  the  number  of  possible  com- 
binations of  this  kind  is,  in  theory,  unlimited,  and  the  num- 
ber of  those  that  are  actually  in  constant  use  is  exceed- 
ingly great.  We  have  before  us  a  work  describing  and 
illustrating  more  than  five  hundred  of  such  elementary 
movements.*  Some  of  these,  especially  such  as  illustrate 
the  most  important  and  fundamental  principles,  will  be  de- 
scribed in  this  chapter.  If  the  reader  will  study  them  at- 
tentively, they  will  not  only  afford  him  a  clearer  general 
insight  into  the  nature  and  workings  of  mechanical  force, 
but  will  aid  him  much  in  understanding  the  construction 
of  such  machinery  as  he  may,  from  time  to  time,  have  op- 
portunity to  examine,  and  will  greatly  increase  his  interest 
in  it. 

One  mode  by  which  mechanical  force  is  transferred  from 
one  revolving  shaft  to  another  is  by  a  band.  These  bands 
are  made  sometimes  of  cords  running  in  grooves,  and  some- 
times of  broad  belts  of  leather,  or  some  similar  substance, 
running  upon  the  wide  pulleys,  being  prevented  from  slip- 
ping upon  them  by  friction.  You  will  often  see  in  large 
manufacturing  establishments  a  long  shaft  placed  near  the 

*  Brown's  Five  Hundred  and  Seven  Mechanical  Movements.  Artisan 
Office,  New  York. 


52    TEANSFEB  OF  FOBCE  BY  PULLEYS  AND  BANDS. 

ceiling,  and  extending  the  whole  length  of  the  apartment, 
with  pulleys  here  and  there  along  the  whole  extent  of  it, 
and  bands  bringing  down  the  force,  so  to  speak,  to  a  great 
variety  of  different  machines  on  the  tables  or  bench- 
es of  the  workmen  below. 

If,  in  such  a  case,  the  motion  is  communicated  by 
what  is  called  an  open  belt  or  band — that  is,  one 
not  crossed,  as  in  Figure  1 — the  motion  of  the  lower 
pulley,  through  the  force  transmitted  from  the  up- 
per one,  and  consequently  that  of  the  shaft  which 
the  lower  one  carries,  will  be  in  the  same  direction 
as  that  of  the  upper  one. 

On  the  other  hand,  if  the  belt  be  crossed, 
the  direction  of  the  motion  will  be  reversed. 

Very  often,  of  course,  the  workman  at  the  shaft 
below  will  wish  to  stop  his  own  particular  machine 
without  interrupting  the  movement  of  the  shaft 
above,  by  which  all  the  other  machines  are  carried 
as  well  as  his  own.  A  contrivance  is  accordingly 
adopted  by  which  the  connection  of  his  machine 

with  the  shaft  above  may  be  suspend-  BELT- 
ed  and  restored  at  pleasure,  which  contriv- 
ance consists  of  what  is  called  the  fast  and 
loose  pulley.  This  is  illustrated  in  the  en- 
graving, Figure  3.  The  pulley  on  the  upper 
shaft,  it  will  be  observed,  is  single,  while  the 
corresponding  one  on  the  lower  shaft  is  double. 
The  upper  pulley  is  fixed  firmly  to  its  shaft, 
and  must  revolve  with  it,  but  the  left  half  of 
FAST  A™  3LoosB  th6  lower  one  is  loose,  while  the  right  half 
POI.LEY.  jg  fasti  Thus,  by  slipping  the  band  from  the 
loose  pulley  to  the  fast  one,  or  from  the  fast  one  to  the 
loose  one  below,  the  machine  driven  by  the  lower  one  may 
be  stopped  or  set  in  motion  at  pleasure  by  the  workman, 


A    EOOM    AT    HAKPER  S. 


53 


without  interfering  with  the  continued  motion  of  tne  great 
shaft  above.  The  pulley  on  the  upper  shaft  is  made  broad 
enough  to  take  the  band  from  either  of  the  pulleys  below. 
In  Figure  3,  the  lower  shaft  is  placed  for  convenience 
quite  near  the  upper  one,  but  in  practice  such  connections 
are  made  by  belts  extending  a  considerable  distance  from 


BUBN16UINO  MAUBLE  PA 


54  TRANSFER    OF    FORCE    BY   PULLEYS    AND   BANDS. 

the  shaft  above  to  the  working  machinery  below,  as  is  in- 
dicated  by  the  break  in  the  belt  shown  in  the  figure. 

A  good  example  of  this  bringing  down  of  the  force  by  a 
long  band  from  a  shaft  above  is  shown  in  the  engraving 
of  the  process  of  burnishing  marble  papers  as  performed 
in  Harper's  establishment. 

The  long  band  on  the  left  is  the  medium  by  which  force 
is  communicated  from  the  shaft  above  to  the  one  below, 
near  the  work,  the  pulley  below  being  double,  one  part  be- 
ing fast  and  the  other  part  loose,  so  that  the  operator  can 
put  in  motion  or  stop  the  burnisher  at  pleasure. 

The  burnisher  is  formed  by  a  highly-polished  surface  at 
the  lower  end  of  the  long  bar  hinged  at  the  ceiling,  and 
worked  to  and  fro  over  the  surface  of  the  sheet  of  paper 
upon  the  table  by  means  of  the  transverse  bar  seen  near 
the  middle  of  the  pictui'e,  which  is  made  alternately  to 
push  and  to  pull  the  burnisher  by  means  of  the  crank  in- 
distinctly seen  to  the  right  of  the  small  fly-wheel  on  the 
lower  shaft.  Thus  this  engraving,  besides  illustrating  the 
form  and  functions  of  a  band  for  conveying  force,  serves 
also  as  an  example  of  the  manner  in  which  a  continuous 
rotary  motion  is  converted  into  a  reciprocating  rectilinear 
one. 

In  the  above-described  cases,  the  two  shafts — one  of  them 
furnishing,  and  the  other  receiving  the  force 
— are  pai'allel  to  each  other.  The  wheel,  how- 
ever, which  is  to  receive  and  be  driven  by  the 
force,  may  have  its  axis  at  right  angles,  or  at 
any  other  angle  to  the  shaft  from  which  its 
force  is  to  be  derived.  All  that  is  necessary 
in  such  a  case  as  this  is  so  to  arrange  the  pul- 
leys that  the  band  can  take  the  direction  indi- 
cated  in  Figure  4. 
ANGLES.  The  nature  of  the  effect  produced  by  the 


REGULATION    OF    SPEED.  55 

transfer  of  force  in  these  ways  from  one  pulley  to  another 
upon  different  shafts  depends  greatly  on  the  comparative 
dimensions — in  circumference — of  the  two  pulleys. 

In  Figure  5,  for  example,  the  upper  pulley, 
we  will  suppose,  is  of  one  half  the  diameter, 
and,  of  course,  of  one  half  the  circumference  of 
the  lower  one.  Let  us  suppose  that  the  cir- 
cumference of  the  upper  one  is  two  feet,  and 
that  of  the  lower  four  feet.  Then  the  upper 
shaft,  in  one  revolution,  will  only  carry  over  two 
feet  in  length  of  the  band.  But  two  feet  in 
length  of  the  band  will  only  carry  the  lower 
pulley  through  one  half  a  revolution,  so  that 
it  will  take  two  revolutions  of  the  upper  shaft 
to  produce  one  of  the  lower. 

On  the  same  principle,  if  the  upper  pulley  is  larger  than 
the  lower  one,  the  revolution  of  the  lower  will  be  propor- 
tionally greater  in  speed.  If  a  wheel  thirty  feet  in  circum- 
ference upon  one  shaft  drives  one  of  three  inches  circum- 
ference on  another,  the  latter  will  make  one  hundred  and 
twenty  revolutions  for  every  one  of  the  former. 

Or  the  process  of  producing  the  acceleration  may  be  di- 
vided, as  it  were,  by  introducing  an  intermediate  shaft. 
For  example,  the  upper  pulley  may  be  ten  times  greater  in 
circumference  than  the  second  one,  which  will  cause  the 
second  one  to  revolve  ten  times  as  fast  as  the  first ;  and 
then  there  may  be  a  pulley  on  this  second  shaft,  with  an- 
other band  connecting  it  with  the  third  shaft,  the  pulleys 
being  in  the  same  proportion — that  is,  ten  to  one.  Thus, 
the  third  shaft  revolving  ten  times  as  fast  as  the  second, 
and  the  second  ten  times  as  fast  as  the  first,  there  will  be 
a  hundred  revolutions  of  the  third  to  every  single  revolu- 
tion of  the  first. 

It  is  very  important  to  remember  that  there  is  no  loss 


56    TRANSFER  OF  FORCE  BY  PULLEYS  AND  BANDS. 

or  gain  whatever  of  force  in  these  transmissions;  for  what 
is  gained  in  speed  is  lost  in  power,  and  what  is  gained  in 
power  is  lost  in  speed.  In  some  cases,  as,  for  instance,  in 
polishing,  great  speed  is  required,  with  but  little  power. 
In  others,  as  in  the  case  of  the  shears  for  cutting  iron  bars, 
as  shown  in  a  former  chapter,  a  slow  motion,  combined  with 
great  power,  is  the  object  to  be  attained ;  and  thus,  in  the 
construction  of  machinery,  the  relative  sizes  of  the  driving 
and  driven  wheels  are  determined  by  the  comparative  de- 
grees of  speed  and  power  required  for  the  purposes  in- 
tended. 

Sometimes  there  is  a  set  of  pul- 
leys of  different  sizes  on  the  upper 
shaft,  with  a  corresponding  set  in 
the  reversed  order  on  the  lower 
one,  so  that  the  band  can  be  shift- 
ed to  any  pair  at  the  pleasure  of 
the  workman,  according  to  the  na- 
ture of  the  work  that  he  has  in 
Fig.  c.  hand.  For  instance,  in  the  case  of 

MEANS   OF  VABYING   6PEKD 

AND  POWEE.  a  lathe,  if  he  has  iron  to  turn,  he 

requires,  while  cutting  away  the  iron,  little  speed  and  great 
power,  and  for  this  purpose  he  carries  the  band  over  the 
pair  of  pulleys  on  the  right,  as  shown  in  the  left-hand  part 
of  the  engraving,  Figure  6.  But  when  he  comes  to  the 
work  of  polishing  the  surface  of  the  iron,  after  it  is  finished 
as  to  its  form,  he  requires  great  speed  and  little  power,  and 
then  he  shifts  the  band  toward  the  pulleys  on  the  left. 
Sometimes  these  systems  of  wheels  are  blended  into  cones, 
as  shown  in  the  right-hand  part  of  the  engraving,  the  rel- 
ative speed  of  the  two  shafts  depending  upon  the  part  of 
the  conical  surfaces  which  the  band  passes  over  for  the 
time  being. 
In  the  large  manufacturing  establishments  of  modern 


DIVISION   AND   DISTRIBUTION    OF   FORCE.  57 

times,  the  quantity  of  force  that  is  transmitted  in  this  way 
by  bands,  and  the  magnitude  of  the  pulleys  and  bands  by 
which  it  is  transmitted,  are  often  enormous.  There  is  an 
account  in  the  newspapers,  at  the  time  of  the  writing  of 
this  chapter,  of  a  pulley  put  up  in  a  mill  in  Fall  River,  Mas- 
sachusetts, twenty- seven  feet  in  diameter,  and  weighing 
over  sixty  tons,  and  also  of  a  belt  of  leather  used  in  a  cer- 
tain mowing-machine  factory  of  such  dimensions  as  to  con- 
sume one  hundred  and  fifty  fades  in  the  manufacture  of  it, 
and  weighing  nearly  a  ton.  The  force  conveyed  by  such 
machinery  as  this  is  sufficient,  when  divided  and  distribu- 
ted among  the  spinning-machines  of  the  mill,  to  drive  from 
fifty  thousand  to  one  hundred  thousand  spindles. 
02 


TRANSFER  OP  FORCE  BY  GEARING. 


CHAPTER  V. 

TRANSFER    OF   FORCE    BY    GEARING. 

BUT,  besides  the  use  of  bands,  there  is  another  mode  of 
connecting  shafts  so  as  to  communicate  force  from  one  to 
another,  and  that  is  by  what  is  called  gearing — that  is,  by 
means  of  notched  wheels,  the  teeth  of 
which  "engage"  with  each  other,  as 
shown  in  Fig.  7.  In  this  case,  as  in  that 
of  the  belt  jor  band,  the  relative  speed  of 
the  two  shafts  will  depend  upon  the  rel- 
ative circumference  of  the  two  wheels, 
as  measured  by  the  number  of  teeth  in  each.  For  example, 
if  in  the  figure  the  left-hand  wheel  is  the  driving  one,  and 
has  thirty  teeth,  while  the  one  on  the  right,  which  is  driven, 
has  forty,  it  is  plain  that  when  the  former  has  made  one 
revolution,  its  thirty  teeth  will  only  have  engaged  with 
and  carried  forward  thirty  of  the  teeth  of  the  large  wheel 
— that  is,  will  have  carried  it  only  through  three  quarters 
of  a  revolution  ;  or,  in  other  words,  that  it  will  take  four 
revolutions  of  the  one  to  produce  three  revolutions  of  the 
other;  but  the  power  with  which  the  shaft  of  the  larger 
wheel  revolves  will  be  proportionally  increased.  Thus  the 
proportion  of  speed  to  power,  in  the  transmission  of  the 
force,  can,  in  this  case,  as  well  as  in  that  of  force  transmit- 
ted by  a  band,  be  regulated  at  pleasure  by  the  comparative 
sizes  of  the  wheels. 

But,  what  is  still  more  curious,  not  only  can  the  whole 
revolution  of  the  shaft  that  is  driven  be  accelerated  or  re- 
tarded by  making  the  wheel  by  which  the  force  is  received 


CHANGE    OF   SPEED.  59 

larger  or  smaller  in  circumference  than  the  one  from  which 
it  receives  it,  but  its  speed  may  be  varied  at  different  por- 
tions of  the  same  revolution  by  varying  the  curvature  of 
different  portions  of  it.  Of  course  the  curvature  of  the 
driving-wheel  must  be  varied  to  correspond,  so  that  the 
distance  from  the  centre  of  one  shaft  to  that  of  the  other 
through  the  two  teeth  which  are  engaged  at  the  several 
successive  moments  of  rotation  shall  be  "  constant" — that 
is,  always  the  same. 

In  Fig.  8,  for  example,  we  have  two 
oval-shaped  wheels  geared  together. 
In  the  position  in  which  they  are 
shown  in  the  engraving,  that  part  of 
the  right-hand  wheel  where  the  curva- 
ture is  gnat — as  if  it  were  a  portion  of  a  small  wheel — is 
engaged  with  a  portion  of  the  left-hand  wheel  where  the 
curvature  is  small,  like  that  of  a  portion  of  a  large  wheel. 
In  this  part  of  the  rotation,  therefore,  if  the  left-hand  wheel 
is  the  </mu??<7-wheel,  the  motion  that  it  would  communi- 
cate would  be  quick ;  but,  as  the  movement  goes  on,  the 
upper  part  of  the  right-hand  wheel,  where  the  curvature  is 
small — making  it  like  a  portion  of  a  large  wheel — is  brought 
into  connection  with  a  portion  of  the  driving-wheel  where 
the  curvature  is  great.  The  motion  of  the  right  wheel 
will  consequently  here  be  quickened.  By  such  an  arrange- 
ment as  this,  therefore,  the  comparative  speed  of  the  two 
wheels  will  be  changed  four  times  in  each  revolution. 

When  the  forms  of  the  wheels  are  not  so  adjusted  that 
the  distance  from  centre  to  centre  through  the  teeth  en- 
gaged is  always  the  same,  then  one  centre  or  the  other 
must  be  movable,  to  allow  this  distance  to  change ;  and  the 
kind  of  motion  thus  imparted  may  be  infinitely  varied,  ac- 
cording to  the  forms  of  the  wheels,  and  the  manner  in 
which  they  bear  upon  each  other.  Thus  the  most  coinpli- 


60          TRANSFER  OF  FORCE  BY  GEARING. 

cated  motions,  or,  rather,  motions  of  any  character  that 
may  be  required,  can  be  derived  from  perfectly  uniform 
rotation,  as,  for  example,  in  Fig. 
9,  where  the  lower  wheel  acts  on 
the  irregular  shaped  one  above. 
Here  the  distance  from  centre  to 
centre  through  the  teeth  that  are 
Fig.  9.  engaged  is  not  constant,  and,  of 

COMPLICATED  MOVEMENT. 

course,  the  centre  of  the  upper  one 

must  rise  and  fall,  carrying  the  bar  with  it  at  every  oscil- 
lation. By  this  means  quite  a  complicated  oscillatory  mo- 
tion is  given  to  the  bar. 

Very  complicated  motion,  both  of  revolution  and  oscilla- 
tion, is  required  for  many  purposes  in  machines.  For  in- 
stance, in  some  forms  of  power  printing-presses  the  move- 
ment must  pause  a  moment  in  a  certain  part  of  its  course 
to  allow  time  for  the  attendant  to  place  the  sheet  of  paper 
to  be  printed  properly  on  the  frame,  and  also  again  in  an- 
other part  to  continue  the  pressure  of  the  types  upon  the 
paper  long  enough  for  the  proper  absorption  of  the  ink 
into  its  texture.  And  so  in  the  manufacture  of  pins.  A 
central  horizontal  wheel  is  provided,  with  a  number  of  bars 
like  spokes,  each  of  which,  as  the  wheel  revolves,  receives 
and  carries  round  a  piece  of  wire  of  the  proper  length  to 
form  the  pin.  There  are  small  subordinate  machines  placed 
around  the  circumference  of  the  central  wheel,  each  of 
which  performs  a  specific  operation,  and,  of  course,  the  cen- 
tral wheel  must  pause  long  enough  at  regular  intervals  to 
allow  these  subsidiary  machines  to  perform  their  appropri- 
ate work,  as  the  pins,  in  the  process  of  formation,  come  suc- 
cessively to  it.  For  instance,  the  wheel  must  pause  an  in- 
stant at  the  beginning  of  its  course,  where  the  wire  is  re- 
ceived, to  give  the  machine  intended  for  that  purpose  time 
to  measure  and  cut  off  the  pi'oper  length  of  wire,  and  then 


COMBINED   MOTIONS.  61 

again  at  the  end  of  the  first  quarter  of  the  revolution,  to 
have  the  point  formed  and  sharpened,  and  at  the  next  to 
have  a  head  put  on,  and  so  on  until  at  the  end  the  pin  is 
dropped  in  a  finished  state  into  its  receptacle.  The  suc- 
cessive motions  and  pauses  thus  required  must  be  given  by 
means  of  proper  forms  in  the  wheels,  by  which  uniform  and 
continuous  rotary  force  is  modified  in  transmission. 

And  so  in  winding  thread  upon  a  spool.  The  spool  must 
revolve,  and  at  the  same  time  move  laterally,  by  just  the 
diameter  of  a  single  thread  at  each  revolution,  in  order  to 
receive  one  layer  of  thread  smoothly  and  regularly  upon 
it;  and  then,  when  the  winding  has  proceeded  once  across 
to  the  farther  end  of  the  spool — the  left-hand  end,  for  ex- 
ample— it  must  reverse  its  lateral  motion,  while  the  rotary 
motion  is  continued  without  interruption,  so  as  to  carry 
the  winding  in  a  second  layer  of  thread  back  to  the  right- 
hand  end.  And  all  this  must  be  done  by  modifying  the  ac- 
tion of  force  absolutely  continuous  in  its  source,  but  mod- 
ified solely  by  the  forms  through  which  it  is  transmitted. 
Sometimes,  however,  the  reverse  of  this  process  is  neces- 
sary— that  is,  the  source  from  which  the  moving  power  is 
derived  is  not  uniform,  and  has  to  be  made  uniform  in  its 
action  by  the  mechanism.  This  is  the  case  in  the  watch, 
and  in  some  clocks,  the  works  of  which  are  carried  by  the 
uncoiling  of  a  spring.  In  this  case,  as  the  process  of  un- 
coiling goes  on,  the  force  becomes  weaker  and  weaker  by 
the  diminishing  elasticity  of  the  spring ;  and  the  diminu- 
tion must  be  compensated  for  by  an  increase  in  the  circum- 
ference of  the  wheel  on 
which  the  force  takes  ef- 
fect, which  result  is  at- 
tained by  a  contrivance 
called  the  barrel  andfu- 

866,    gllOWH     ill    Fig.   10. 


62  TRANSFER    OF   FORCE    BY    GEARING. 

The  coiled  spring  is  contained  in  the  barrel,  and  the  chain 
which  conveys  the  force  turns  the  fusee,  the  circumference 
of  which  is  formed  in  a  spiral,  so  that  the  portion  of  the 
circumference  which  is  acted  upon  continually  enlarges  it- 
self as  the  spring  uncoils. 

In  all  the  preceding  cases  the  axis  of  the  two  wheels 
transmitting  and  receiving  force  are  par- 
allel to  each  other.  When  they  are  at 
!llimfilllllll»-i  right  angles  to  each  other,  the  teeth  of 
one  of  them  are  sometimes  formed  upon 
a  kind  of  rim  or  margin,  at  right  angles 
to  the  plane  of  the  wheel,  making  a 
crown,  as  it  were,  from  which  circum- 
stance such  a  wheel  is  called  a  crown 

OROWl?  WHEEL.  wJl6el. 

Another  mode  by  which  motion  may  be  transmitted  from 
one  axis  to  another  at  right  angles  to  it,  or,  indeed,  at  any 
other  angle,  is  by  beveling  the  margins  of  the  wheels  in 
the  part  where  the  teeth  are  to  be  cut,  so 
that  they  may  engage  each  other  at  the 
desired  angle,  whatever  it  may  be. 

In  all  cases  of  the  transmission  of  mo- 
tion in  machinery  by  means  of  wheels 
having  projections  engaging  with  each 
other,  the  projections  are  called  tect/i 
when  they  are  formed  by  cuttings  in  the 
substance  of  the  wheel  itself,  as  in  the 
works  of  a  watch.  But  when  they  are  formed  of  some 
other  substance — of  iron,  for  instance,  or  a  harder  kind  of 
wood  inserted  in  a  wooden  wheel,  as  is  common  in  mill- 
work,  they  are  called  cogs. 

Sometimes,  instead  of  two  wheels  that  engage  with  each 
other  by  means  of  teeth  or  cogs,  it  is  a  wheel  and  straight 
bar  that  are  geared  together,  by  which  means  a  rotary  ia 


RECIPROCATING   MOVEMENTS. 


63 


Fig.  14. 

BEOIPROOATING  MOVEMENT. 


converted  into  a  rectilinear  mo- 
tion. This  arrangement,  shown 
in  Fig.  13,  is  called  a  rack  and 
pinion.  In  Fig.  14  there  is  rack- 
work  on  each  side,  the  pinion 
being  in  the  centre,  and  the  pin- 
ion has  teeth  only  upon  one  half 
the  circumference.  The  effect,  as 
will  be  seen  by  an  attentive  con- 
sideration of  the  figure,  will  be, 
that  if  the  pinion  has  a  direct  motion — that  is,  a  motion  in 
the  direction  of  the  hands  of  a  watch,  when  the  toothed 
part  of  it  engages  with  the  rack-work  on  the  lower  side,  it 
will  move  the  frame  toward  the  left,  and  then,  when  this 
same  toothed  part  comes  round  to  the  upper  rack-work,  it 
will  throw  it  to  the  right.  Thus  a  continued  rotary  mo- 
tion will  be  transformed  into  a  reciprocating  rectilinear 
one. 

Sometimes  cogs  or  teeth  are  placed  on  the  interior  of 
the  circumference  of  a  wheel,  in  which  case  the  action  when 
in  gear  is  the  reverse  of  that  which 
is  produced  when  they  are  on  the 
outside.  For  instance,  the  lower 
of  the  two  small  wheels  in  Fig.  15 
being  the  driving-wheel,  its  teeth 
work  into  the  teeth  which  extend 
half  round  the  centre-piece  of  the 
large  wheel, until,  when  they  come 
to  the  end  of  these  teeth,  they  en- 

FOBWABD  AND  BEVEBSE  MOTION,  gage  with  the  teeth  on  the  inter- 
nal surface  of  the  outer  rim  of  the  wheel,  and  carry  the 
large  wheel  in  the  contrary  direction.  Thus  the  continued 
and  equable  motion  of  the  driving-wheel  will  carry  the 
large  one  round  slowly  and  with  great  force  through  half 


64 


TRANSFER   OF   FORCE   BY   GEARING. 


Fig.  16. 

CHAIN  AND  PCX.I.EY. 


a  revolution,  and  then  bring  it  back  again  with  a  swift  mo- 
tion and  small  force  to  its  first  position. 

The  communication  of  motion  by  means  of  belts  or  bands, 
and  by  toothed  wheels,  would  seem  to  be  essentially  differ- 
ent in  their  nature,  and  yet  they  may  be  in  a  measure  com- 
bined, though  in  such  case  the 
band  must  take  the  form  of  a 
chain  of  some  sort,  with  iron  pro- 
jections to  engage  with  recesses 
formed  to  receive  them  in  the 
circumference  of  the  wheel,  as  in 
Fig.  16,  or  with  openings  to  re- 
ceive teeth  or  cogs  formed  in  the 
circumference  of  the  wheel,  as  in 
Fig.  17. 

In  some  cases,  however,  as  in  that  of  the 
barrel  and  fusee  in  the  works  of  a  watch, 
a  flexible  chain  is  used  to  transmit  motion 
without  any  teeth,  either  upon  the  pulley 
or  upon  the  chain,  the  nature  of  the  con- 
nection rendering  such  an  arrangement 
unnecessary.  The  case  of  the  barrel  and 
fusee,  already 
shown,  is  an  ex- 
ample of  this  kind. 

In  Fig.  1 8  we  have  an  example 
of  single-toothed  driving-wheels. 
The  effect  is  evidently  to  impel 
the  driven  wheel  only  one  step 
in  its  movement  at  every  revolu- 
tion of  the  driver.  Thus,  while 
the  latter  revolves  with  a  con- 
tinuous and  equable  motion,  the 
dNOLE-TooTno)  wnEKL8.  former  advances  by  a  series  of 


Fig.  IT. 

AXOTHKU  FOEM. 


CURIOUS   EXAMPLES. 


65 


impulses,  with  intervals  of  rest  between.    There  are  a  great 
many  cases  in  which  devices  of  this  kind  are  employed. 

An  eccentric  wheel  is  a  wheel  revolving  about  a  point 
which  is  not  in  the  centre  of  it,  so  that  it  bulges  out,  as  it 
were,  on  one  side.  If  such  a  wheel  is  inclosed  within  an- 
other, which  is  connected  with  a  bar  that  is  so  arranged  as 
to  allow  of  a  sliding  motion  from  side  to  side,  the  eccentric, 
or  cam,  as  it  is  sometimes  called,  will 
give  it  a  reciprocating  lateral  motion, 
as  shown  in  Fig.  19,  where  the  wheel 
in  the  centre,  revolving  on  the  axis  on 
the  right  side  of  it,  will,  as  it  revolves, 
push  the  circular  frame  surrounding 
it,  and  the  bar  seen  on  the  left  con- 


and  then  the  other,  as  the  bulge  goes  round. 

Curious  examples  of  the  pur- 
poses which  eccentric  wheels 
are  sometimes  employed  to  sub- 
serve are  given  in  Fig.  20.  In 
the  first  example  a  single  cam 
works  the  upper  jaw  of  a  pair 
of  shears  for  cutting  off  bars  of 
iron,  as  shown  in  a  previous  en- 


graving; and  in  the  second  there 
are  two  cams  upon  the  same 
axis,  which  alternately  raise  and 
depress  the  bars  on  which  they 
act,  for  the  purpose  of  opening 
and  closing  different  valves  al- 
ternately with  each  other,  or  for 
producing  any  other  alternating 
motion. 


Fig.  20. 

ACTION   OF  TUB   CAM. 


Sometimes  teeth  are  formed  upon  wheels  so  as  to  act  as 


66 


TRANSFER  OF  FORCE  BY  GEARING. 


cams,  or,  rather,  as  portions  of  different  cams  arranged 
around  the  same  axis,  as  shown  in  the  arrangement  for 

working  a  trip-ham- 
mer  m  Fig.  21,  where 
the  ponderous  trip- 
hammer A,  turning  on 
the  joint  seen  at  the 
right,  is  lifted  by  the 
series  of  cams  ar- 
ranged around  the  ax- 
is B.  The  hammer  is 
raised  by  the  teeth  as  the  axis  revolves,  and  let  fall  in  a 
succession  of  blows  upon  the  mass  of  hot  iron  seen  on  the 
anvil  at  the  left.  Teeth  operating  in  this  way  are  some- 
times called  wipers. 

In  Fig.  22  we  see  another  form 
of  what  are  called  wipers,  which, 
by  the  rotation  of  the  axis  to 
which  they  are  attached,  in  the 
direction  of  the  ar;ow,  impel  the 
frame  surrounding  them  alter- 
nately to  the  right  and  to  the 
left,  thus  producing  a  reciproca- 
ting rectilinear  motion  from  a  continuous  rotary  one.  The 
same  effect  is  produced  by  a  dif- 
ferent contrivance,  involving  the 
use  of  what  is  called  a  crank-pin. 
The  crank-pin  is  seen  in  section 
near  the  right-hand  margin  of  the 
wheel,  and  as  the  wheel  revolves 
it  moves  up  and  dowrn  in  the 
groove,  or  "  slot,"  as  it  is  called, 
in  the  arm,  at  the  same  time  car- 
rying the  arm  alternately  to  and 


ACTION    OP   A   LOCOMOTIVE    ENGINE. 


67 


fro,  and  thus  communicating  a  reciprocating  rectilinear 
movement  to  the  bar  below  by  means  of  the  rack  and 
toothed  section — that  is,  the  toothed  portion  of  a  wheel. 

It  is  precisely  the  reverse  of  this  effect  that  is  often  re- 
quired— that  is,  a  reciprocating  rectilinear  motion  is  to  be 
converted  into  a  continuous  rotary  one — and  this  is  almost 
always  the  case  in  the  use  of  the  steam-engine  for  supply- 
ing the  force  required.  In  the  case  of  the  locomotive  en- 
gine, for  example,  the  movement  of  the  piston  to  and  fro  is 
made  through  the  medium  of  a  crank,  to  turn  the  driving- 
wheels  by  which  the  train  is  drawn  along  the  track.  The 
connection  of  the  machinery  by  means  of  which  this  effect 
is  produced  is  usually  observable  by  the  by-stander  in  any 
locomotive  as  seen  upon  a  track ;  but  it  is  very  plainly 


G8 


TRANSFER  OP  FORCE  BY  GEARING. 


manifest  in  the  preceding  engraving,  representing  the  sim- 
pler form  of  machinery  that  was  employed  when  the  sys- 
tem was  first  introduced. 

By  proper  combinations  of  these  and  many  other  ele- 
ments of  machinery,  an  infinite  number  and  variety  of  ef- 
fects may  be  produced  as  the  exigencies  of  the  work  to  be 
accomplished  may  require.  Indeed,  there  are  some  con- 
trivances that  seem  to  be  almost  endued  with  intelligence, 
as  they  find  out  for  themselves,  as  it  were,  what  is  required, 
and  vary  their  action  as  the  exigencies  of  the  case  vary. 
This  kind  of  action,  which  takes  effect  in  one  way  or  an- 
other, or  at  one  time  or  another,  as  the 
emergency  requires,  is  called  automatic. 
An  example  of  it  is  shown  in  Fig.  24,  which 
represents  what  is  called  the  governor  of 
a  steam-engine.  The  horizontal  axis  be- 
low, and  the  beveled  gearing,  bring  the 
force  from  the  engine,  and  cause  the  verti- 
cal axis  carrying  the  two  heavy  wheels  to 
revolve.  The  upper  end  of  the  vertical 
axis  is  connected  with  the  valve  which  ad- 
mits the  steam  from  the  boiler  to  the  en- 
gine. When  the  machinery  goes  too  fast,  the  balls,  by  too 
rapid  revolution,  spread  as  they  revolve,  and  draw  down 
the  bar  above  by  shortening  the  diamond-shaped  frame  be- 
tween the  balls  and  the  bar,  and  thus  partially  closing  the 
valve  and  diminishing  the  flow  of  the  steam.  On  the  other 
hand,  when  the  machinery  goes  too  slowly,  the  balls  fall  a 
little  way  together,  and  push  up  the  bar,  so  as  to  open  the 
valve  a  little  more.  Thus  the  contrivance  watches,  as  it 
were,  the  passage  of  the  steam,  and,  by  an  automatic  move- 
ment, checks  the  supply  when  it  is  too  great,  and  increases 
it  when  it  is  too  small. 


Fig.  24. 

AUTOMATIC  ACTION. 


THE   PATENT-OFFICE.  69 

The  examples  given  in  this  and  the  preceding  chapter 
will  be  sufficient  to  give  the  reader  some  general  idea  of 
the  nature  and  character  of  the  contrivances  by  which  mo- 
tion is  transmitted  in  machinery,  and  changed  in  certain 
respects  by  the  mode  of  its  transmission.  They  are  not 
sufficient,  however,  to  convey  any  idea  of  the  immense  num- 
ber and  variety  of  these  contrivances.  The  number  of  com- 
binations, each  distinct  in  certain  essential  points  from  any 
other,  as  described  in  books,  or  exemplified  in  models  in 
the  collections  of  patent-offices,  or  as  actually  working  in 
machine-shops  and  manufactories  all  over  the  country,  is 
beyond  all  calculation,  and  is  increasing  now  every  year 
faster  than  ever  before.  From  five  hundred  to  a  thousand 
new  contrivances  are  brought  forward  every  month  in  the 
patent-office  at  Washington,  a  very  large  proportion  of 
which  are  new  combinations  for  changing  the  character 
and  action  of  mechanical  force  by  the  mode  of  its  trans- 
mission, so  as  to  take  it  in  a  simple  form  from  the  piston- 
rod  of  a  steam-engine,  or  the  walking  of  a  horse,  or  the 
turning  of  a  crank  by  the  hands  of  a  man,  or  the  rotation 
of  a  shaft  near  the  ceiling  in  a  work-shop,  and  so  dividing 
it,  and  diverting  and  employing  the  various  portions  into 
which  it  is  divided,  as  to  accomplish  the  most  minute  and 
complicated  operations.  Every  reader  of  this  book  will 
find  innumerable  examples  of  this  kind  of  action  all  around 
him,  and  the  illustrations  given  in  these  chapters  will  per- 
haps lead  him  to  take  an  interest  in  them,  and  aid  him  in 
understanding  them. 

But  the  main  thing  to  be  learned  from  this  chapter  is  the 
fundamental  principle  that  by  none  of  these  contrivances, 
nor  by  any  conceivable  ones,  can  force  be  increased  or  di- 
minished in  amount.  What  is  imparted  to  the  machine  at 
the  beginning  may  be  changed  in  form  and  action,  but  it 
can  not  be  increased  or  diminished  in  quantity.  It  can  be 


70          TRANSFER  OF  FORCE  BY  GEARING. 

accumulated  or  it  can  be  dispersed ;  a  weak  rapid  motion 
can  be  changed  by  the  manner  of  transmitting  it  to  a  slow 
and  powerful  one,  or  a  great  power  moving  slowly  may  be 
made  to  communicate  great  speed  with  small  power,  but 
the  amount  will  be  in  both  cases  the  same. 

When,  therefore,  we  hear  of  any  new  mechanical  con- 
trivance, the  first  and  most  important  inquiry  is,  From  what 
source  is  the  force  to  come  by  which  it  is  to  be  driven? 
There  have  been  a  great  many  attempts,  for  example,  to 
contrive  wings  by  which  a  man  might  fly.  The  engraving 


WINGS  WITHOUT  FORCE   TO    WORK   THEM. 


gives  a  representation  of  one  of  them.  The  difficulty  with 
this  and  with  all  other  similar  contrivances  is  not  that  the 
wings,  if  worked  with  sufficient  rapidity  and  power,  would 
not  suffice  to  sustain  the  weight  of  the  man,  but  that  there 
is  not  in  the  action  of  the  muscles  of  the  human  arms  and 
legs  force  enough  to  work  them  with  that  degree  of  rapidity 
and  power.  Birds  possess— in  the  muscles  of  the  breast, 


WHY   BALLOONS   CAN   NOT   BE   MANAGED. 


71 


by  which  the  wings  are  moved,  and  in  certain  peculiar- 
ities of  the  digestive  organs  which  fit  them  for  drawing 
abundant  and  rapid  supplies  of  force  from  their  food — the 
requisite  strength  for  lifting  themselves  from  the  ground 
and  impelling  themselves  forward  by  strokes  upon  the  air; 
and  if  the  structure  of  the  human  body  were  such  as  to 
give  man  the  command  of  a  force  as  great  in  proportion  to 
iiis  weight  as  that  which  the  hawk  or  the  eagle  wields,  in- 


MURE    WINGS   WITI1OUT    FOKCE. 


72          TRANSFER  OF  FORCE  BY  GEARING. 

genious  mechanics  would  find  very  little  difficulty  in  con» 
triving  wings  by  which  he  could  apply  it. 

It  is  the  same  in  respect  to  navigating  the  air  by  means 
of  a  balloon  in  any  other  direction  than  that  of  the  wind. 
Many  people  think  that  the  thing  to  be  discovered  is  some 
method  of  steering  the  balloon.  But  there  is  no  difficulty 
at  all  in  the  steering — that  is,  in  directing  any  particular 
point  of  it  in  the  way  we  wish  it  to  go.  The  difficulty  is 
in  the  want  of  force  to  make  it  go  forward  in  thatway.  It 
is  propelling,  not  steering  power  that  is  really  required. 

Let  the  reader,  then,  fix  in  his  mind  as  a  fundamental 
principle  that  every  human  mechanism  must  derive  all  the 
force  it  can  possibly  bring  into  action  from  some  one  of  the 
external  som-ces  of  supply  existing  in  nature.  This  the 
mechanism  can  not  increase,  nor  can  it  diminish  it,  but 
must  pass  it  all  on  to  be  expended  in  the  work  done,  or 
diffused  among  the  surrounding  substances  in  the  heat  pro- 
duced by  friction. 

If  there  were  two  new  plans  proposed  for  the  construc- 
tion of  a  cotton-mill,  in  one  of  which  there  was  a  claim  that 
the  inventor  had  discovered  a  mode  of  generating,  out  of 
nothing,  the  force  by  which  the  mill  was  to  be  driven,  and 
in  the  other  that  his  machine  would  make  out  of  nothing 
the  cotton  needed  to  supply  it,  the  two  projects  would  be 
exactly  equal  in  absurdity. 


MESSAGE   TO   KICK.  73 


CHAPTER  VI. 

THE    MILL. 

ONE  morning,  toward  the  spring  of  the  year,  John,  on 
his  way  to  school,  finding  that  he  had  a  little  time  to  spare, 
went  round  by  the  way  of  Lawrence's  shop  to  see  what  his 
cousin  was  doing.  He  found  him  engaged  in  cutting  out 
little  squares  of  thin  glass  with  a  diamond,  for  the  purpose 
of  making  slides  for  his  microscope.  After  remaining  and 
talking  with  him  a  few  minutes,  taking  out  his  watch  fre- 
quently as  he  did  so,  so  as  to  be  sure  not  to  stay  too  long, 
he  finally  said, 

"  Well,  good-by,  Lawrence." 

"Must  you  go?"  asked  Lawrence. 

"  Yes,"  said  John ;  "  I  make  it  a  point  always  to  be  at 
school  on  time" 

So  Lawrence  bid  him  good  morning,  and  he  went  away. 

Just  as  he  was  going  out  of  the  gate,  however,  John 
heard  Lawrence's  voice  calling  to  him.  He  stopped  to 
hear  what  his  cousin  had  to  say. 

"  I  want  you  to  take  a  message  for  me  to  Rick." 

"  Well,  what  is  it?"  asked  John. 

"  Tell  him  I  should  like  to  have  him  inquire  of  some  farm- 
er— if  he  knows  any  farmer — what  is  the  very  hardest  and 
toughest  kind  of  timber  that  grows  in  the  woods  about 
here." 

"  Well,"  replied  John,  in  a  doubtful  and  hesitating  man- 
ner, "I  will  ask  him,  but  I  don't  believe  it  will  do  any 
good." 

"Tell  him  that  if  he  can  find  out  what  is  the  best  wood," 
D 


74  THE    MILL. 

added  Lawrence, "  and  will  go  with  me  and  get  some,  and 
will  help  me  to  turn  some  bats  out  of  it — say  four — he 
shall  have  half  of  them." 

"  Well,"  said  John, "  I'll  tell  him." 

So  John  walked  away. 

That  day,  at  recess,  John,  seeing  Rick  standing  by  him- 
self, apparently  waiting  for  somebody  or  something,  rec- 
ollected his  message,  and  called  to  him. 

"  Rick,"  said  he, "  I've  got  a  message  for  yon  from  Law- 
rence. He  wants  you  to  ask  some  farmer  what  is  the  very 
hardest  and  toughest  wood  that  grows  about  here,  so  as  to 
get  some  of  it  to  make  bats  of." 

Rick  stared  at  him  a  moment  with  a  stupid  expression 
of  countenance,  and  Avith  his  hands  in  his  pockets,  and  then 
said,  in  a  sulky  and  almost  contemptuous  tone, 

"7" don't  know  any  farmer  about  here." 

John  paused  a  moment  on  receiving  this  rebuff,  eying 
Rick  with  a  ludicrous  expression  of  uncertainty  in  his  coun- 
tenance, as  if  he  was  at  a  loss  what  to  do  or  say  next.  At 
length  he  added, 

"He  says  if  you  will  find  out  what  is  the  best  wood,  and 
will  help  him  to  get  it  and  to  make  three  or  four  bats,  you 
shall  have  half  of  them." 

To  this  Rick  made  no  reply,  but  only  stared  at  John  in 
a  bewildered  manner;  and  John,  after  waiting  a  moment, 
turned  round  and  went  slowly  away,  saying  to  himself,  "I 
knew  it  wouldn't  be  of  any  use." 

Very  soon  the  person  that  Rick  was  waiting  for  came, 
and  Rick  went  away  with  him,  and  thought  no  more  for 
a  time  about  the  message  he  had  received.  That  afternoon, 
however,  he  happened  to  see  a  farmer  coming  into  the  yard 
at  Morningside  with  a  load  of  wood.  The  farmer  stopped 
at  the  end  of  a  long  wood  pile,  and  began  unloading  it. 
Seeing  this  man  and  his  load  of  wood  reminded  Rick  of  his 


KICK   AND   THE    FARMER.  75 

message ;  and  as  it  just  then  occurred  to  him,  too,  that  it 
would  be  a  nice  thing  to  have  two  new  bats  of  a  specially 
hard  wood,  he  determined  to  take  this  opportunity  to  make 
the  inquiry.  So  he  called  out  to  the  man, 

"  Say !  you  mister  !  what's  the  hardest  kind  of  wood  that 
grows  hereabouts  ?" 

The  man  looked  up  a  moment  from  his  work,  and,  seeing 
that  it  was  Rick,  did  not  answer,  but  went  on  unloading 
his  wood.  Rick's  character  as  a  mischievous  and  ugly  boy 
was  well  known  to  all  the  people  that  came  to  Morningside, 
and  every  one  wished  to  have  as  little  to  do  with  him  as 
possible.  The  farmer  thought  that  Rick,  in  asking  the 
question,  had  some  plan  of  quizzing  him,  or  playing  upon 
him  some  kind  of  trick,  or  offering  him  some  impertinence, 
so  he  said  nothing. 

"  Say  !"  repeated  Rick ;  "  tell  us,  won't  ye  ?" 

The  man,  being  very  sure  that  Rick  was  not  serious  in 
his  inquiry,  but  was  designing,  in  some  way  or  other,  to 
make  a  fool  of  him,  had  a  great  mind  to  pay  him  in  his  own 
coin,  and  answer  "  poplar,"  which  is  perhaps  the  very  soft- 
est and  weakest  wood  that  grows,  and  the  most  unsuitable 
for  bats,  or  axe-handles,  or  wedges,  or  any  thing  of  the  kind. 
But  he  thought  that,  on  the  whole,  it  was  best  not  to  ex- 
cite Rick's  ill  will,  and  so  he  said,  after  a  moment's  pause, 
but  without  stopping  his  work, 

"Well, I  suppose  hornbeam  is  about  the  hardest  wood 
that  grows  hereabouts." 

Rick,  on  hearing  this  answer,  stood  for  a  moment  with 
his  hands  in  his  pockets  staring  at  the  man  in  a  somewhat 
stupid  manner,  while  the  farmer  went  on  quietly  with  his 
work  of  unloading  his  sled,  until  presently  Rick  asked, 

"  Say  !  how  shall  we  know  hornbeam  when  we  see  it  ?" 

"  Know  it?"  repeated  the  farmer,  still  going  on  with  his 
work ;  "  why,  by  the  looks  of  it." 


76  THE    MILL. 

Rick  stared  at  the  man  a  moment  more,  as  if  hardly 
knowing  whether  this  was  meant  to  be  a  serious  answer 
or  not,  and  then  finally  asked, 

"  Yes ;  but  how  does  it  look  ?" 

"  How  does  it  look  :"  repeated  the  farmer  j  "  why,  like 
hornbeam." 

If  Rick  had  been  accustomed  to  any  nicety  of  observa- 
tion, he  would  have  perceived  a  faint  semblance  of  a  smile 
lurking  at  the  corners  of  the  farmer's  mouth  as  he  said  this; 
but,. though  his  senses  had  been  trained  to  extraordinary 
accuracy  in  watching  the  approach  of  a  ball  through  the 
air,  and  in  so  regulating  the  swing  of  the  bat  that  it  should 
strike  the  ball  at  the  precise  instant  and  at  the  precise  dis- 
tance from  the  end  of  the  bat  required  for  producing  the 
greatest  effect,  his  perceptions  were  far  from  being  quick 
in  any  other  respects.  So  he  attributed  the  farmer's  ab- 
surd replies  to  boorish  stupidity,  and  turned  away  mutter- 
ing to  himself, "  What  a  fool !" 

On  reflecting  upon  the  subject  of  Lawrence's  proposal, 
Rick  concluded  that  he  should  like  two  new  bats  very 
much,  especially  if  they  were  made  of  a  particularly  hard 
kind  of  wood,  and  accordingly,  after  school,  he  ran  to  the 
gate,  and  called  out  to  John  as  he  was  going  down  the 
road  toward  home.  John  looked  around  to  see  what  was 
wanted. 

"  Tell  him,"  said  Rick, "  it's  hornbeam,  and  I'm  agreed 
to  go." 

In  consequence  of  this  and  subsequent  arrangements,  on 
the  next  Saturday  Lawrence,  Rick,  and  John  met  at  an  ap- 
pointed place  of  rendezvous,  and  set  out  on  an  excursion 
in  search  of  some  hornbeam.  They  had  provided  them- 
selves with  a  handsaw  and  a  small  axe,  their  intention  be- 
ing to  saw  off  the  hornbeam,  if  they  should  find  any  of  the 
right  length  for  bats,  and  to  hew  out  the  sticks  pretty  near- 


THE    SLUICE-WAT.  77 

Iy  to  the  right  size,  so  as  to  have  as  little  useless  wood  as 
possible  to  bring  home. 

It  was  a  pleasant  day  in  March,  and  there  was  still  a  good 
deal  of  snow  upon  the  ground,  especially  in  the  fields  and 
woods,  but  it  was  well  worn  down  in  the  roads.  After  go- 
ing on  for  some  distance,  taking  a  direction  which  led  to- 
ward a  region  of  forests,  they  came  to  a  mill,  and  Law- 
rence said  that,  as  the  mill-men  would  be  likely  to  know 
where  they  could  find  hornbeam  growing,  he  would  go  in 
and  inquire  of  them.  But  before  he  went  into  the  mill  the 
attention  of  all  three  of  the  party  was  attracted  to  the 
other  side  of  the  stream  on  which  the  mill  stood,  where 
some  workmen  were  making  a  sluice-way,  or  flume,  to  con- 
vey the  water  down  to  a  site  below,  where  it  seems  a  new 
mill  was  to  be  built. 

There  were  two  gangs  of  men  at  work  upon  this  sluice- 
way. One  of  them  was  employed  in  bailing  out  the  water 
from  a  part  which  had  already  been  excavated,  aiid  pour- 
ing it  into  a  tub  which  stood  upon  the  top  of  the  bank, 
from  which  tub  it  flowed  into  a  long  wooden  conduit,  by 
which  it  was  conveyed  down  into  the  mill-stream  below. 
The  others  were  hoisting  up  a  great  stone  from  the  bottom 
of  the  excavation  by  some  kind  of  hoisting  apparatus,  form- 
ed of  pulleys  and  ropes,  and  worked  by  a  windlass  at  the 
foot  of  it. 

The  boys,  being  somewhat  interested  in  these  operations, 
went  over  to  watch  them  for  a  few  moments,  and  presently 
they  all  three  went  down  the  bank,  and,  finding  a  good 
seat  there  in  a  warm,  sunny  place,  they  sat  down  to  rest 
themselves  and  talk. 

"There,"  said  Rick,  pointing  as  he  spoke  at  the  men 
who  were  raising  the  big  stone,  "  you  said  there  could 
not  be  any  gain  of  force  in  machinery ;  but  see  how  those 
two  men  lift  that  big  stone  by  the  tackle  and  fall.  They 


THE    MILL. 


r 


could  not  lift  a  stone  one  quarter  as  big  by  their  own 
strength.  .It  is  the  tackle  and  fall  that  does  it.  The  force 
is  in  that." 

"  That  is  very  true,"  said  Lawrence ;  "  at  least  it  is  very 
true  in  a  certain  sense.  I  don't  see  how  it  would  be  pos- 
sible for  two  men  to  get  so  big  a  stone  out  of  such  a  deep 
ditch  without  a  tackle  and  fall,  or  some  other  such  con- 
trivance." 

The  first  thing  to  be  done  when  you  undertake  to  give 
a  person  any  instruction,  and  especially  when  you  attempt 
to  correct  any  mistaken  ideas  he  may  have  formed,  is  to 
bring  his  mind  into  harmony  with  your  own  by  seeing  and 
acknowledging  whatever  of  truth,  or  semblance  of  truth, 
there  may  be  in  the  erroneous  opinion  he  expresses ;  for  in 
almost  all  the  beliefs  and  opinions  which  people  hold  there 
is  some  truth,  or  at  least  some  semblance  of  truth,  and  this 


CALCULATIONS.  79 

is  really  what  the  mistaken  person  sees  and  assents  to. 
"Whenever,  therefore,  we  wish  to  make  a  person  see  a  thing 
as  we  see  it,  the  first  step  we  have  to  take  is  to  see  it  our- 
selves as  he  sees  it. 

"The  windlass  and  the  tackle  and  fall  help  the  men  a 
great  deal,  it  is  true,"  said  Lawrence,  "  but,  after  all,  they 
only  help  them  by  storing  and  concentrating  the  force 
which  the  men  put  into  the  apparatus,  and  not  by  really 
increasing  it.  You  see  they  are  turning  the  windlass  by 
a  long-handled  crank.  How  long  do  you  think  that  crank 
is,  John — I  mean  the  arm  from  the  centre  out  to  the  han- 
dle?" 

John  estimated  the  length  at  about  a  foot. 

"That's  about  right,  I  should  think,"  said  Lawrence. 
"Well,  double  the  arm  would  be  the  diameter  of  the  circle 
that  the  hands  of  the  men  move  through  in  turning  the 
windlass  once  round ;  and  as  the  circumference  of  a  circle 
is  about  three  times  the  diameter,  the  men's  arms  must 
make  a  sweep  of  about  six  feet  at  every  turn,  and  in  ten 
turns  they  must  carry  the  handles  round  and  round  a  dis- 
tance of  sixty  feet,  for  ten  times  six,  you  know,  Rick,  is 
sixty." 

Rick  assented. 

"And  now,"  said  Lawrence, "  let  us  notice  how  high  the 
stone  is  at  a  particular  moment,  and  then  wait  till  the  men 
have  turned  the  windlass  ten  times — that  is,  till  they  have 
exerted  their  strength  through  a  space  of  sixty  feet,  and 
then  see  how  high  the  stone  has  been  raised.  You  count 
the  turns,  Rick." 

So  Rick  counted  up  to  ten,  and  both  the  boys  were  sur- 
prised to  see  how  little  the  stone  had  ascended. 

"  So,  you  see,"  said  Lawrence,  "  that,  in  one  sense,  there 
is  no  real  gain  in  the  employment  of  such  machinery.  In 
another  sense  there  is  a  gain — that  is,  there  is  an  advant- 


80  THE  MILL. 

age,  but  there  is  no  actual  gain  of  force.  All  the  force 
which  the  men  can  impart  by  a  movement  through  sixty 
feet  of  space  is  concentrated  in  a  movement  of  the  stone 
through  one  or  two  feet.  So  you  see  that  while  there  is 
really  a  great  gain,  in  the  sense  of  advantage  or  benefit,  in 
the  use  of  such  a  contrivance  as  this,  the  advantage  con- 
sists in  concentrating  and  accumulating  the  force  which 
the  men  exert,  and  not  at  all  in  increasing  the  amount 
of  it. 

"And  now,"  continued  Lawrence,  turning  the  conversa- 
tion to  another  point,  not  wishing  to  fatigue  Rick's  mind 
by  confining  his  attention  too  long  to  one  train  of  thought, 
"  look  at  that  tub  upon  the  top  of  the  bank  that  the  other 
men  are  pouring  the  water  into  from  the  bottom  of  the 
ditch.  The  water,  you  see,  runs  out  through  an  opening 
near  the  bottom -of  the  tub,  and  so  down  the  spout  into  the 
stream." 

"What  do  they  have  a  tub  and  a  spout  for  ?"  asked  Rick. 
"Why  don't  they  pour  the  water  right  out  upon  the  ground, 
and  so  let  it  run  down  the  bank." 

"  Perhaps  they  don't  wish  to  have  the  bank  washed 
away,"  replied  Lawrence, "  so  they  place  a  wooden  spout 
there  to  convey  the  water  safely  over  it  down  to  the  stream 
below.  And  I  suppose  that  they  have  a  tub  at  the  top, 
because  it  is  so  much  more  easy  to  pour  the  water  into  a 
tub  than  it  would  be  to  pour  it  into  the  end  of  the  trough. 
They  require  some  kind  of  receptacle  for  it  to  take  it  by 
pailfuls  as  they  dip  it  up,  and  deliver  it  in  a  steady  stream 
into  the  spout.  Don't  you  see  that,  though  the  men  pour 
the  water  in  at  intervals  into  the  tub,  it  flows  in  quite  a 
regular  stream  out  of  the  lower  end  of  the  spout  where  it 
falls  into  the  river  ?" 

Lawrence  then  went  on  to  explain  that  the  whole  ar- 
rangement, in  its  action  upon  the  water,  was  quite  similar 


THE    CREATION    OF   FORCE    IMPOSSIBLE.  81 

to  that  of  the  grindstone  in  its  action  upon  force.  The 
grindstone  receives  the  force  in  a  succession  of  separate 
impulses  given  to  it  by  the  weight  of  the  foot  upon  the 
end  of  the  treadle  at  regular  intervals,  but  the  stone,  by  its 
weight,  receives  and  stores  this  force,  and  delivers  it  at  the 
outer  margin  of  the  stone,  when  the  tool  is  pressed  upon 
it,  in  a  steady  and  continuous  action,  just  as  the  arrange- 
ment of  the  tub  and  spout  receives  the  water  in  a  succes- 
sion of  separate  pourings  from  the  pails,  and  delivers  it  at 
the  end  of  the  spout  in  a  steady  and  continuous  flow. 

"And  just  as  there  can  not  be  any  more  water,"  he  add- 
ed, in  conclusion, "  to  flow  out  at  the  end  of  the  spout  than 
is  poured  into  the  tub  from  the  pails,  so  there  can  not  be 
any  more  force  exerted  by  the  grit  of  the  surface  of  the 
grindstone  upon  the  tools,  in  its  total  amount,  than  is  put 
into  it  by  the  successive  impulses  of  which  the  weight,  or, 
rather,  the  pressure  of  the  grinder's  foot  upon  the  treadle, 
imparts  to  it.  And  so  witli  all  other  machinery.  It  can 
only  use  force  supplied  to  it.  It  can  not  create  any." 

This  effect  of  producing  a  steady  and  equal  flow  of  wa- 
ter from  a  source  furnishing  it  in  a  series  of  distinct  and  in- 
termittent supplies  is  sometimes  produced  in  a  very  differ- 
ent manner  from  that  exemplified  by  the  tub  and  wooden 
channel  in  this  case.  The  most  common  mode  is  by  what 
is  called  an  air-chamber,  which  consists  simply  of  a  strong 
metallic  receptacle  for  confined  air,  which  receives  and 
stores  the  impulsive  force  by  its  elasticity,  and  delivers  it 
in  a  comparatively  steady  flow.  They  use  this  contriv- 
ance in  the  case  of  fire-engines,  whether  worked  by  hand 
or  by  steam.  It  is  necessary,  for  the  most  efficient  ac- 
tion of  the  engine  in  putting  out  the  fire,  that  the  water 
should  issue  from  the  pipe  in  a  steady  stream,  and  not  in 
a  succession  of  jets.  Now,  as  the  action  of  the  men  in 
working  the  brakes,  and  that  of  the  engine  in  impelling  the 
D2 


82 


THE    MILL. 


piston-rod,  drives  the  water  forward  by  a  series  of  separate 
impulses,  it  would  be  delivered  from  the  pipe  in  a  succes- 
sion of  jets  were  it  not  that  there  is  always  an  air-chamber 
of  copper  or  brass — usually  to  be  seen  rising  above  the 
machine  in  the  form  of  a  big  inverted  bottle — which  is  con- 
nected by  its  mouth  at  the  lower  end  with  the  pipe  which 
conveys  the  water,  so  that  the  excess  of  force  given  by 
each  succeeding  stroke  of  the  brakes,  or  of  the  piston,  is 
absorbed  in  condensing  the  air  in  the  air-chamber,  and  this 
excess  of  force  is  given  out  again  in  the  intervals  between 
the  strokes.  Thus  what  would  otherwise  be  a  succession 
of  jets  is  ti-ansformed  into  a  steady  stream.  The  action 
is  exceedingly  rapid,  but  the  effect  is  very  sure  and  very 
decisive. 

But  to  return  to  our  party.  While  they  sat  looking  at 
the  water  as  it  glided  down  the  long  spout,  and  issued  in 
quite  a  little  cascade  at  the  bottom,  John  said  that  he 
should  have  liked  very  much,  when  he  was  a  boy,  to  have 
such  a  fall  as  that  to  put  in  a  wheel  for  a  wTater-mill. 

"  You  might  put  in  quite  a  nice  little  wheel  there  at  the 
lower  end  of  the  spout,"  said  Lawrence — "  an  undershot 
wheel." 

"  What  is  an  under- 
shot wheel  ?"  asked  John. 
"It  is  a  wheel,"  said 
Lawrence,  "so  made  and 
so  placed  that  the  wa- 
ter shoots  under  it,  and 
causes  it  to  revolve  by 
the  force  with  which  it 
strikes  against  the  floats 
or  paddles  projecting 
from  the  wheel.  But  a 
wheel  in  such  a  fall  as 


UNDERSHOT   WHEEL. 


FORCE    OP   FALLING   WATER.  83 

this-  would  not  revolve  with  much  force.  It  would  be 
a  pretty  thing  enough  for  a  plaything,  but  you  could  not 
make  it  do  much  work." 

The  degree  of  force  which  a  stream  of  water  exerts,  or, 
rather,  is  capable  of  exerting  in  all  such  cases  as  this,  de- 
pends upon  a  very  simple  principle,  which  is  not  only  of 
fundamental  importance  in  all  the  calculations  of  millmen 
and  engineers,  but  is  so  simple  that  it  is  very  easily  under- 
stood by  any  young  person  who  will  attentively  consider 
it  a  few  minutes.  The  force  depends  in  its  amount  on  two 
elements — first,  the  quantity  of  water ;  and,  secondly,  the 
height  from  which  it  falls.  And  it  makes  no  difference 
whether  it  falls  perpendicularly  or  flows  down  an  inclined 
plane,  provided  it  encounters  no  resistance  in  coming  down 
the  plane.  It  is  true  that,  practically,  it  must  in  all  cases 
meet  with  more  or  less  resistance  from  the  friction  upon 
the  plane  or  upon  the  sides  of  the  channel  which  confines 
it.  In  such  a  case  as  this  which  Lawrence  was  speaking 
of,  for  example,  the  friction  of  the  water  upon  the  sides  of 
the  spout  would  retard  the  motion,  and  so  diminish  the 
force  to  a  very  perceptible  degree ;  and  in  the  case  of  a 
brook  running  over  a  stony  bottom  down  a  mountain 
gorge,  the  whole  of  the  falling  force  of  the  water  would 
perhaps  be  spent  as  fast  as  it  was  generated,  so  that  the 
water  would  impinge  against  the  stones  which  lay  in  its 
bed  at  the  bottom  of  the  descent  with  no  greater  force 
than  it  did  against  those  at  the  beginning  of  it. 

But  in  all  cases  where  the  energy  of  the  action  is  not 
thus  spent  in  friction  or  in  collisions  by  the  way,  the  force 
with  which  it  strikes  at  the  bottom  of  any  fall,  or  that  with 
which  it  issues  from  any  opening  at  the  bottom  of  a  re- 
ceptacle holding  it,  depends  simply  on  the  quantity  of  wa- 
ter which  thus  flows  or  issues  in  a  given  time,  and  on  the 
height  from  which  it  falls,  or,  in  the  case  of  flowing  from 


84  THE    MILL. 

an  orifice,  on  the  depth  or  distance  of  the  orifice  below 
the  surface.  This  makes  the  calculations  in  respect  to  the 
absolute  theoretical  force  of  water  used  for  driving  ma- 
chines very  plain  and  easy  for  millmen  and  engineers. 
They  have  only  to  consider  the  quantity  of  water — that 
is,  the  weight  of  what  falls  or  flows  out  in  a  given  time — 
and  the  height  from  which  it  falls,  or  the  depth  which  pro- 
duces the  pressure  under  which  it  issues. 

Thus,  in  the  case  of  the  tub  and  the  spout  which  the 
boys  had  been  observing,  if  the  bank  had  been  ten  feet 
high,  and  if  each  man  had  dipped  up  two  half  pailfuls  in  a 
minute,  the  force  that  the  stream  would  exert  upon  John's 
supposed  water-wheel  at  the  bottom  would  be  the  force 
of  two  pailsful  of  water  falling  through  ten  feet,  provided, 
of  course,  there  had  been  absolutely  no  friction  or  other 
obstruction  by  the  way. 

Lawrence  did  not  attempt  to  explain  this  fully  to  Rick 
and  John,  for  he  thought  that  Rick  was  not  probably  far 
enough  advanced  in  his  capacity  for  understanding  gener- 
alizations of  this  kind  to  take  an  interest  in  such  a  train 
of  thought.  He  explained  it  afterward  to  John,  who  was 
old  enough  and  far  advanced  enough  to  take  a  great  in- 
terest in  it.  He  explained  to  him  that,  as  the  force  with 
which  the  water  shot  under  a  wheel  was  the  same  as  that 
which  it  would  exert  by  its  weight  in  falling  from  the 
same  height  directly  down,  there  was  no  difference  in  the- 
ory between  employing  the  force  of  the  water  to  act  by 
its  impulse  in  striking  the  floats  of  the  wheel  on  the  lower 
side  of  it — as  shown  in  the  engraving  of  an  undershot 
wheel — or  by  its  weight  in  descending  directly  in  boxes 
or  buckets  formed  in  the  circumference  of  the  wheel  to 
contain  it,  as  is  shown  in  the  case  of  what  is  called  an 
overshot  wheel,  such  as  is  represented  in  the  following  en 
graving. 


CASE    SUPPOSED. 


85 


OVERSHOT   WHI 


But,  though  there  is  no  differ- 
ence in  theory,  that  is,  in  the 
actual  amount  of  force  devel- 
oped in  the  two  cases,  there  is 
a  great  difference  in  the  avail- 
ability of  the  two  methods  of 
employing  it,  making  it  much 
better  in  some  cases  to  employ 
an  overshot,  and  in  others  an 
undershot  wheel. 

After  a  short  tinie  Lawrence  and  the  boys  rose  from 
their  seats  and  went  up  the  bank.  Lawrence  went  into 
the  mill  to  make  his  inquiries,  while  John  and  Rick  stood 
on  the  shore  above  the  mill  to  look  at  the  dam  and  the  wa- 
ter flowing  over  it,  and  the  great  pond  of  still  water  which 
spread  from  side  to  side,  and  extended  far  up  a  winding 
and  wooded  valley.  Presently  Lawrence  came  out  and 
said  he  had  found  out  which  way  to  go.  So  they  went  on 
along  the  road,  and  as  they  went  Lawrence  thought  that 
he  would  try  the  experiment  of  presenting  to  the  boys  a 
train  of  thought  in  respect  to  force,  with  a  view  of  seeing 
whether  he  could  lead  Rick  to  take  an  interest  in  it  by 
means  of  making  the  images  involved  such  as  Rick  could 
easily  picture  to  his  imagination. 

"  Suppose,"  said  he, "  that  there  was  a  thunder-cloud  up 
in  the  air  that  contained  water  enough,  if  it  was  all  col- 
lected, to  make  a  hundred  hogsheads,  and  that  it  was  at 
the  height  of — how  high  do  you  suppose  a  thunder-cloud 
commonly  is, Rick?" 

Rick  said  he  had  no  idea. 

"  We  often  read  of  mountains  eight  or  ten  thousand  feet 
high,"  said  Lawrence,  "and  of  thunder- clouds  half  way 
down  their  sides.  We  will  suppose,  therefore,  that  the 
thunder-cloud  is  five  thousand  feet  high ;  that  is  not  far 


86  THE    MILL. 

from  a  mile.  Then  the  whole  amount  of  force  which  would 
be  developed  by  the  shower,  from  the  cloud  where  it  be- 
gins to  fall  down  to  the  sea,  which  all  the  water  reaches  at 
last,  would  be  that  of  a  hundred  hogsheads  of  water  falling 
a  mile." 

"  But  there  could  not  be  any  hogsheads  of  water  at  all 
in  a  cloud,"  said  Rick. 

"  No,"  said  Lawrence,  "not  in  that  form;  but  there  might 
be  drops  enough  to  make  a  hundred  hogsheads ;  or,  if  there 
were  not  drops  enough  already  formed,  there  might  be  va- 
pors enough  to  form  them." 

"  Well,  go  ahead,"  said  Rick. 

"Now,  as  there  are  one  hundred  hogsheads  of  water  a 
mile  high  in  the  air,  there  is  stored  in  them,  or  held  by 
them,  as  it  were,  in  reserve,  as  I  was  saying,  a  falling  force 
represented  by  the  weight  of  all  that  water  falling  a  mile, 
which  is  something  enormous.  Now  let  us  follow  the  wa- 
ter in  imagination  as  it  comes  down,  and  see  what  becomes 
of  all  this  force." 

Lawrence  was  interrupted  in  the  work  of  presenting  his 
"train  of  thought,"  as  he  called  it,  by  observing  that  Rick 
had  stopped  by  the  wayside,  and  was  looking  up  very  in- 
tently into  an  evergreen  tree  which  was  standing  there 
near  the  road.  He  and  John  stopped  too. 

"What  is  it?"  asked  John. 

"  I  believe  I  see  a  bird's  nest,"  said  Rick. 

"Never  mind,"  said  John ;  "  it  can't  be  any  thing  but  a 
last-year's  bird's  nest,  at  any  rate ;  it  is  too  early  for  any 
of  this  year's,  so  come  along." 

"  I  mean  to  climb  up  and  see,"  said  Rick. 

"  Yes,"  said  Lawrence,"  I  would  if  I  were  you ;  it  is  well 
to  be  sure ;  and,  besides,  I  want  to  see  how  well  you  can 
climb." 


MR.  BERRY.  87 

So  Rick  climbed  up  into  the  tree,  and  found  that  it  was, 
as  John  had  predicted,  nothing  but  an  old  nest. 

"  I'm  glad  I  went  up,  at  any  rate,"  said  Rick,  as  he  came 
down. 

Lawrence  was  glad  of  the  incident  too,  for  it  showed 
him  how  little  interest  Rick  took  in  what  he  had  been  say- 
ing. The  gaining  of  any  new  ideas  on  the  subject  of  force 
had  less  attraction  for  him,  it  seemed,  than  even  a  last- 
year's  bird's  nest !  And  though  he  would  have  been  bet- 
ter pleased  if  Rick  had  evinced  some  interest  in  what  he 
was  saying,  yet  still,  since  he  did  not  feel  any  interest,  he 
wished  to  know  that  fact.  He  was  glad  to  have  any  thing 
occur  to  make  known  to  him  what  the  true  state  of  the 
case  was. 

Just  as  Rick  had  descended  from  the  tree,  and  was  brush- 
ing off  the  dust  and  the  fragments  of  bark  from  his  clothes, 
a  sled  loaded  with  wood  appeared,  as  it  was  coming  along 
the  road.  A  man  was  walking  by  the  side  of  the  oxen, 
and,  as  he  came  nearer,  he  proved  to  be  the  same  farmer 
that  had  given  Rick  such  equivocal  answers  about  horn- 
beam. His  name  was  Berry,  and  his  house  was  very  near 
the  woods  to  which  Lawrence  had  been  directed  at  the 
mill. 

"  Ah !"  said  Lawrence, "  here  comes  Mr.  Berry.  The  place 
where  we  are  going  is  on  his  land,  and  he  will  tell  us  ex- 
actly where  to  go ;  besides,  I  was  intending  to  stop  at  his 
house  and  ask  his  permission  to  cut  down  one  of  his  horn- 
beam-trees." 

"  You  won't  get  any  thing  out  of  him,"  said  Rick ;  "  he's 
an  old  fool." 

But  Mr.  Berry  proved  himself  not  to  be  a  fool  at  all,  on 
coming  to  the  spot.  When  he  saw  that  the  leader  of  the 
party  of  young  people  was  Lawrence — whom  he  knew  very 
well,  in  some  degree  personally,  but  more  by  reputation — 


88  THE    MILL. 

and  observing  that  Lawrence  wished  to  speak  with  him, 
he  stopped,  allowing  his  oxen,  however,  to  go  steadily  on 
with  their  load. 

He  told  Lawrence  exactly  where  to  go  on  his  land,  and 
gave  him  permission  to  cut  what  hornbeam  he  wanted. 

"  If  you  will  call  at  my  house,"  said  he, "  and  take  my 
boy  Charley  along  with  you,  he  will  show  you  just  where 
to  go." 

Lawrence  thanked  him,  and  said  he  should  be  glad  to  do 
so,  and  then  Mr.  Berry  went  on.  Very  soon,  however,  he 
stopped  again,  and,  turning  round,  said, 

"  Look  here,  Mr.  Wollaston !  what  you  cut  in  the  woods 
will  be  green,  and  it  will  take  some  time  to  season  it.  I 
have  got  some  in  my  loft  all  ready — some  that  I  got  out 
for  axe-handles ;  I  keep  a  good  supply  on  hand,  so  as  to 
have  it  well  seasoned  when  I  want  it.  If  you  prefer  it 
seasoned,  you  can  take  some  of  mine — as  much  as  you  want 
— only  put  in  its  place  the  same  amount  of  green,  to  keep 
my  supply  good ;  it  will  get  dry  by  the  time  I  want  any." 

Lawrence  thanked  Mr.  Berry,  and  then  he  and  the  boys 
went  on.  They  found  Charley,  and  he — first  showing  them 
the  store  of  seasoned  hornbeam  sticks  which  Mr.  Berry  had 
in  his  loft,  among  which  the  boys  found  several  of  the  right 
size  for  their  purpose — led  the  way  into  the  woods.  Law- 
rence, under  his  direction,  soon  found  some  hornbeam-trees, 
the  stems  of  which  were  large  enough  to  be  sawed  or  split 
in  two  through  the  centre,  and  to  furnish  wood  sufficiently 
thick  to  form  a  bat  out  of  each  half.  Lawrence  concluded 
to  cut  wood  enough  for  four  bats,  and  to  exchange  two  of 
them  for  two  seasoned  pieces  from  Mr.  Berry's  stores. 

He  had,however,  just  begun  the  work  when  Rick's  atten- 
tion was  attracted  by  a  large  gray  squirrel  which  he  saw 
running  along  a  log. 

"My  eyes!"  he  exclaimed;  "there's  a  gray  squirrel — a 


RICK   AFTER   A   SQUIRREL.  89 

splendid  fellow !  See !  see !  He's  worth — oh,  if  I  could 
only  catch  him !" 

"  Never  mind  him,"  said  John ;  "  you  can't  possibly  catch 
him — not  alive." 

"If  I  can't  get  him  alive,"  said  Rick,  "lean  get  him  dead. 
I  want  his  skin.  Give  me  a  club." 

So  saying,  he  began  to  look  about  the  ground  in  a  state 
of  great  excitement  in  search  of  a  club.  He  soon  found  a 
stick,  and,  seizing  it,  he  ran  off  after  his  prize.  The  squir- 
rel bounded  from  the  log  to  the  trunk  of  a  tree,  ran  up  the 
tree  to  a  branch,  crept  out  to  the  end  of  the  branch,  and 
leaped  across  into  another  tree,  and  from  that  to  another, 
and  another.  Rick  followed  him  in  a  state  of  great  excite- 
ment. There  were  many  evergreens  in  that  part  of  the 
wood,  the  foliage  of  which  was  so  dense  that  Rick,  in  the 
eagerness  of  his  chase,  soon  disappeared  from  view,  and 
they  saw  him  no  more.  He  did  not  return. 

In  the  mean  time  Lawrence  and  John  went  on  with  their 
work.  They  cut  down  the  tree  which  they  had  selected, 
and  from  it,  by  means  of  the  small  axe  and  the  saw,  they 
fashioned,  in  the  rough,  four  pieces  of  wood  of  suitable  form 
and  size  to  make  either  bats  or  axe-handles,  as  might  be  re- 
quired. Returning  then  with  Charley  to  Mr.  Berry's  house, 
they  exchanged  two  of  their  pieces  for  two  of  the  same  size 
that  were  seasoned,  and  then  set  out  for  home. 


90  FALLING   FORCE. 


CHAPTER  VII. 

FALLING    FORCE. 

As  these  books  are  not  intended  for  children,  nor  even 
for  boys  as  old  as  Rick  unless  their  thinking  and  reasoning 
powers  are  much  more  fully  developed  than  his  were,  it  is 
to  be  hoped  that  most  of  the  readers  of  it  may  feel  some 
interest  in  hearing  Lawrence's  explanation  of  the  phenom- 
ena attending  the  progress  of  the  vast  quantity  of  water 
sometimes  contained  in  a  cloud,  in  its  course  from  the  sky 
to  the  tops  of  the  hills  and  mountains,  and  from  the  tops 
of  the  hills  and  mountains  to  the  sea.  The  substance  of 
his  explanation,  as  he  made  it  to  John  while  they  were 
walking  along  together  on  their  way  home,  was  as  follows: 

If  we  suppose,  as  Lawrence  did,  in  fact,  that  the  weight 
of  a  hogshead  of  water  is  two  hundred  pounds,  the  hundred 
hogsheads  would  weigh  twenty  thousand  pounds;  and  if 
we  also  suppose  the  height  from  which  it  Avould  fall — that 
is,  the  distance  from  the  height  of  the  cloud  to  the  level  of 
the  sea — to  be  five  thousand  feet,  the  whole  amount  of 
falling  force  would  be  one  hundred  millions  of  foot-pounds! 

But  what  is  a  foot-pound '?  It  is  the  force  generated  by 
the  falling  of  one  pound  one  foot.  Take  a  cannon  ball,  or 
a  stone,  or  any  other  heavy  substance  weighing  one  pound, 
and,  holding  it  one  foot  above  the  table,  let  it  drop.  The 
force  imparted  to  it  by  gravitation  during  its  fall,  and 
which  has  to  be  extinguished  as  mechanical  force  when  it 
strikes  the  table,  leaving  out  of  view  for  the  present  the 
resistance  of  the  air,  is  one  foot-pound — that  is,  the  falling 
force  of  one  pound  through  a  space  of  one  foot.  If  you 


MEASUREMENT   OP  FORCE.  91 

hold  your  hand  upon  the  table  and  let  the  weight  descend 
upon  it,  your  hand  sustains  a  blow  of  one  foot-pound. 

If  you  throw  a  pound  ball,  or  a  stone  weighing  a  pound, 
against  a  wall  so  that  it  strikes  the  wall  with  precisely  the 
same  force  that  the  falling  ball  under  the  above-mentioned 
conditions  would  strike  a  table,  the  force  with  which  it 
strikes  is  one  foot-pound. 

On  the  same  principle,  if  the  mass  of  stone  or  iron  let 
fall  weighs  two  pounds,  the  force  developed  is  two  foot- 
pounds ;  and  also,  if  the  one  pound  weight  is  let  fall  two 
feet,  the  force  generated  would  be  two  foot-pounds.  If  it 
falls  one  hundred  feet,  the  force  generated  is  one  hundred 
foot-pounds. 

And  inasmuch  as  the  force  imparted  by  gravitation  to  a 
descending  weight  through  a  given  space  is  the  same  as 
that  which  would  be  abstracted  from  one  ascending  through 
the  same  space,  it  requires  an  upward  force  of  one  hundred 
foot-pounds — leaving,  as  before,  the  resistance  of  the  air  out 
of  the  account — to  throw  a  pound  ball  up  one  hundred  feet. 

If  a  ball-player  has  a  ball  weighing  a  quarter  of  a  pound, 
and  knocks  it  with  a  force  sufficient  to  cause  it  to  ascend 
perpendicularly  a  hundred  feet,  the  force  imparted  by  his 
blow  is  that  of  twenty-five  foot-pounds. 

Such  is  the  mode  by  which  forces  of  this  kind  are  de- 
noted among  English-speaking  nations.  On  the  Continent 
of  Europe,  where  the  French  language  extensively  prevails, 
the  unit  of  length  being  the  metre,  and  that  of  weight  being 
the  kilogramme,  the  unit  employed  for  denoting  this  kind 
of  force  is  the  fcilogranunetre,  which,  of  course,  means  the 
force  of  one  kilogramme  falling  through  a  space  of  one 
metre.  Now,  as  a  kilogramme  is  a  little  more  than  twice 
the  weight  of  a  pound,  and  as  a  metre  is  more  than  three 
times  the  length  of  a  foot,  the  French  kilogrammetre  is 
more  than  six  times  the  English  foot-pound. 


92  FALLING   FORCE. 

In  the  above  examples  the  resistance  of  the  air  is  left 
out  of  the  account.  This  resistance  would  be  very  small 
in  the  case  of  a  ball  of  iron  falling  one  foot  upon  a  table 
or  upon  the  ground,  but  it  would  be  much  greater  in  the 
case  of  a  ball  of  wood  or  of  cork  which  should  have  the 
same  weight;  for  the  ball  of  wood  or  of  cork,  in  order  to 
weigh  the  same  as  the  ball  of  iron,  would  necessarily  be 
many  times  as  large,  and,  consequently,  have  to  encounter 
and  displace  a  much  larger  quantity  of  air.  Now  the  re- 
sistance of  the  air  in  such  a  case  is  in  proportion  to  the 
amount  displaced  to  open  a  passage  for  the  falling  body, 
and  to  the  surface  exposed  to  friction  along  the  sides  of  it. 
In  the  case  of  small  masses  of  iron  or  stone,  therefore,  but 
a  very  small  part  of  the  falling  force  would  be  absorbed  by 
the  air,  while  in  the  case  of  very  light  substances,  such  as 
feathers  or  flakes  of  snow,  almost  the  whole  of  the  force 
imparted  by  gravitation  would  be  absorbed  as  fast  as  it  is 
generated,  so  that  such  substances  always  descend  with  a 
very  slow  motion.  The  force  flows  out  of  them,  as  it  were, 
as  fast  as  it  is  received,  and  so  their  motion  is  but  little  ac- 
celerated. That  the  resistance  of  the  air  is  the  real  cause 
of  the  slow  descent  of  such  bodies  is  proved  positively  by 
the  fact  that  when  the  air  is  removed,  as  it  can  easily  be, 
from  a  tall  glass  jar,  the  lightest  substances  are  found  to 
fall  as  swiftly,  and  to  strike  with  the  same  force  in  propor- 
tion to  their  weight,  as  heavy  ones;  so  that  the  force  with 
which  a  pound  of  snow  in  flakes — which  descend  so  gently 
through  the  air — would,  if  the  air  were  not  present,  strike 
the  ground  with  a  force  which,  combined,  Avould  make  ex- 
actly one  foot-pound. 

The  reader  will  now  understand  exactly  what  Lawrence 
meant  when  he  said  that  in  the  whole  descent  of  one  hun- 
dred hogsheads  of  water  from  a  height  of  five  thousand 
feet — which  is  about  one  mile — above  the  level  of  the  sea, 


FALLING    WATER.  93 

down  to  that  level,  a  force  of  one  hundred  millions  of  foot- 
pounds would  be  generated. 

Let  us  now  follow  the  course  of  such  a  mass  of  water  in 
such  a  fall,  and  see  exactly  how  this  force  is  disposed  of. 

While  the  water  remains  in  a  state  of  vapor  it  may  be 
actually  lighter  than  the  air,  and  so  have  no  tendency  to 
fall ;  or,  rather,  to  speak  more  accurately,  whatever  tend- 
ency it  may  have  toward  the  earth  may  be  counteracted 
by  a  slightly  greater  weight  of  the  air  beneath  and  around 
it  tending  to  buoy  it  up.  As  the  vapor  begins  to  be  con- 
densed, however,  and  to  form  minute  misty  drops,  a  tend- 
ency to  fall  is  at  once  produced,  for  liquid  water,  however 
minute  are  the  masses  of  it,  is  heavier  than  the  air;  but 
when  the  masses  are  very  minute  this  tendency  is  almost 
overpowered  by  the  resistance  of  the  air,  and  may  be  en- 
tirely overpowered  if  the  currents  of  air  in  which  they  are 
floating  have  a  slightly  ascending  motion. 

The  reason  why  very  minute  globules  of  water  like  those 
of  a  mist  or  a  fog  tend  to  fall  so  much  more  slowly  than 
larger  ones  like  those  which  form  drops  of  rain,  is  because 
they  have  so  much  more  surface  in  proportion  to  their 
weight,  and  the  resistance  of  the  air  to  a  body  falling 
through  it  is,  in  a  great  measure,  proportioned  to  the  sur- 
face; and  just  as  it  would  take  more  leather  to  cover  four 
one  quarter  pound  balls  than  to  cover  one  ball  of  the 
weight  of  a  pound,  so  a  million  of  drops,  each  one  contain- 
ing a  millionth  of  a  grain,  would  present  a  vastly  greater 
surface  to  the  air  to  retard  their  descent  than  a  single  drop 
containing  the  whole  quantity  of  water  in  one. 

As,  however,  the  minute  drops  increase  in  size  by  addi- 
tional condensation,  or  by  uniting  with  each  other  so  as  to 
bring  two  or  more  into  one,  they  begin  slowly  to  descend. 
At  first  they  expend  all  their  falling  force  in  overcoming 
the  resistance  of  the  atmosphere — that  is,  in  pushing  the 


94  FALLING    FORCE. 

particles  of  the  atmosphere  out  of  the  way;  or,  to  express 
it  in  more  philosophical  language,  the  motion  which  is  gen- 
erated in  them  by  the  falling  force  is  imparted  to  the  par- 
ticles of  air,  and  so  far  as  there  is  absolute  stoppage  of  mo- 
tion by  minute  frictions  and  collisions  the  force  is  converted 
into  heat,  as  will  be  shown  more  clearly  in  another  chapter. 

As  the  drops  grow  larger  they  descend  more  and  more 
rapidly,  increasing  all  the  time  in  magnitude  as  they  de- 
scend, until  at  length  the  falling  force  becomes  far  more 
than  sufficient  to  open  a  passage  for  them  through  the  air. 
All  this  surplus  of  force  remains  in  them,  of  course,  to  be 
delivered  on  the  ground  below,  when  they  reach  it,  so  that, 
when  at  length  they  fall  upon  the  ground,  they  do  so  with 
all  the  falling  force  which  has  been  generated  by  their  de- 
scent from  the  clouds,  except  what  they  have  distributed 
through  the  air  in  heating  it  and  imparting  motion  to  its 
particles  on  the  way. 

Let  us  now  suppose  that  the  shower  which  we  are  con- 
densing falls  upon  an  elevated  tract  of  land,  consisting  of 
hills  and  mountains  of  such  magnitude  that  the  average 
height  of  the  land  is  one  thousand  feet,  so  that  the  water, 
in  the  whole  of  its  descent  from  the  clouds,  will  have  fall- 
en, upon  an  average,  four  thousand  feet.  So  much,  there- 
fore, of  the  falling  force  of  the  hundred  hogsheads  will  have 
been  expended  On  the  way,  or  suddenly  extinguished  by 
the  impact  of  the  drops  upon  the  ground.  This  extinguish- 
ing of  the  force  is  not,  as  will  hereafter  appear,  an  annihila- 
tion of  it,  but  only  a  change  of  it  into  another  form,  name- 
ly, heat.  At  any  rate,  the  water  loses  it  in  the  form  of 
force,  and  only  retains  such  a  portion  of  the  heat  which  is 
developed  by  the  collisions  as  happens  to  fall  to  its  share. 
The  falling  force  of  that  four  thousand  feet  of  descent  is 
gone  entirely,  which  you  will  find,  on  making  the  calcula- 
tion, amounts  to  eighty  millions  of  foot-pounds  out  of  the 


FALLING    FORCE    IN   THE    STREAMS.  95 

hundred  millions  of  the  whole  descent;  that  is  to  say,  four 
fifths  of  it,  only  one  fifth  of  the  whole  amount  remaining 
to  be  developed  by  the  falling  flow  of  the  water  down  the 
mountains  to  the  sea. 

Such  is  the  enormous  force  that  a  falling  shower  of  this 
magnitude  would  exert  in  its  descent  to  the  upland  on 
which  it  falls,  a  part  being  distributed  through  the  air  on 
its  way,  and  a  part  extinguished  as  force  by  the  impact  of 
the  drops  upon  the  ground. 

In  the  case  of  a  snow-storm,  consisting  of  light  fleecy 
flakes,  the  largest  part  of  this  immense  force  would  be  ex- 
pended in  the  air  on  the  way ;  but  in  case  of  a  rain-shower, 
consisting  of  large  drops,  a  very  considerable  portion  of  it 
would  be  delivered  up  to  the  ground  at  the  end  of  its  fall. 

But,  though  eighty  millions  of  foot-pounds  of  the  falling 
force  of  the  rain  has  thus,  in  our  supposed  case,  been  dissi- 
pated and  lost  at  the  time  the  water  reaches  the  ground, 
there  is  still  twenty  millions  more  to  be  developed  by  the 
remaining  portion  of  the  descent.  Let  us  follow  the  wa- 
ter in  its  course,  and  see  what  becomes  of  this  remainder. 

The  little  streamlets  and  rills  formed  by  the  rain  begin 
at  once  to  flow  down  the  mountain  sides,  and  to  run  along 
the  valley,  each  portion  of  the  water  that  amounts  to  a 
pound  in  weight  developing  a  force  of  one  foot-pound  for 
every"  foot  of  its  perpendicular  descent.  But  this  force,  as 
fast  as  it  is  developed,  is  given  out  to  the  stones,  and  roots, 
and  other  obstructions  which  form  the  beds  of  the  brook- 
lets down  which  it  flows. 

After  descending  in  this  manner  from  the  highland  re- 
gion, rippling  among  the  stones  in  mountain  brooks,  or 
tumbling  over  long  cascades,  the  water  reaches  at  last  the 
more  level  country,  from  which  the  descent  is  gradual  to 
the  sea.  The  brooks  and  rivulets  unite  together  wto  larger 
streams  on  the  way,  and  then  finally  combine  to  form  a 


96  FALLING   FORCE. 

great  river,  which  now  flows  somewhat  smoothly  and  com- 
paratively slowly  toward  the  sea,  with  only  the  force  of  a 
gentle  descent  to  urge  it  along.  If,  for  example,  the  in- 
clination of  its  bed  was  five  feet  to  the  mile,  every  cubic 
foot  of  water  would  have  a  falling  force  of  five  foot-pounds 
to  carry  it  a  mile,  which  amount  offeree  could  only  impart 
to  it  quite  a  moderate  amount  of  motion.  A  boy  walking 
along  the  bank  could  perhaps  easily  keep  up  with  the  cur- 
rent which  this  amount  of  force  would  produce.  A  great 
part  of  this  force,  too,  would  be  expended  on  the  way  in  the 
friction  of  the  water  along  the  bank,  and  in  encounters 
with  rocks,  snags,  roots,  and  other  obstacles  which  it  would 
meet  with  in  its  course,  so  that  after  flowing  onward  for 
several  miles  the  rapidity  of  its  flow  might  not  be  at  all 
increased,  and  might  even  be  diminished,  as  it  is  only  the 
excess  of  the  falling  force  over  the  resistance  and  the  fric- 
tion which  can  operate  to  produce  an  acceleration  of  the 
flow. 

It  would  be,  moreover,  but  a  comparatively  small  por- 
tion of  the  water  which  fell  from  the  cloud  that  would  have 
found  its  way  to  the  channel  of  the  river.  A  large  part  of 
it  would  have  remained  upon  the  surface  of  the  ground, 
adhering  to  the  leaves,  the  grass,  and  the  soil,  and  would 
have  evaporated  when  the  sun  came  out,  after  the  shower 
was  over,  and  so  carried  back  again  into  the  air,  to  form 
the  material  for  future  showers.  Another  part  would  have 
gone  into  the  ground,  there  to  be  absorbed  by  the  roots  of 
plants,  or  would  have  percolated  through  the  strata  of 
sand  and  gravel,  or  through  the  crevices  of  the  rocks,  to 
find  its  way  out  again  in  springs  and  swamps  far  below. 
We  will  suppose  that  half  of  the  whole  amount  reaches  the 
river,  and  at  the  place  where  the  river  began  to  flow  with 
a  smooth^nd  equable  current,  the  bed  of  it  is  five  hundred 
feet  above  the  level  of  the  sea.  We  then  have  a  weight 


TUE    FLOW    OF   TUB    KIVEK.  97 

equal  to  that  of  fifty  hogsheads  that  is  yet  to  fall  five  hun- 
dred feet,  which  is  all  the  force  that  can  possibly  be  gen- 
erated by  the  water  of  this  shower  in  its  whole  course  from 
the  point  we  have  designated  to  the  sea. 

Now,  so  long  as  the  river  flows  over  an  unobstructed 
bed  with  a  gentle  inclination,  the  falling  force  comes  very 
slowly  into  action,  and  a  large  part  of  it  is  absorbed  by  the 
friction  of  the  banks  and  other  sources  of  diversion.  Still, 
a  considerable  amount  of  the  force  imparted  to  it  by  grav- 
itation remains,  and  bears  the  water  along  with  a  certain 
degree  of  momentum,  a  portion  of  which  may  be  abstracted 
and  utilized  by  means  of  a  water-wheel  attached  to  an 
anchored  boat,  for  example.  By  this  means  a  kind  of  float- 
ing mill  may  be  worked,  and  made  to  carry  light  machinery 
by  the  impulse  of  the  flowing  water.  This  force,  however, 
can  not  be  very  great,  for  it  consists  of  that  part  only  of 
the  force  that  has  been  imparted  to  the  waters  by  its  pre- 
vious fall,  which  has  not  yet  been  dissipated  by  friction  and 
collisions. 

By-and-by,  however  the  river  arrives,  we  will  suppose, 
at  a  place  where,  on  account  of  a  sudden  descent  of  the 
land,  there  is  a  fall  of  the  waters  of  perhaps  fifty  feet  in  the 
course  of  half  a  mile.  Here,  of  course,  there  is  a  sudden 
and  great  development  of  the  falling  force  of  the  water, 
shown  by  the  violence  with  which  it  tumbles  over  the  rocks 
along  the  cascade,  and  the  foam  and  the  spray  which  it 
creates  by  its  collisions  with  them.  If  we  suppose  that  the 
quantity  of  water  of  our  original  hundred  hogsheads  now 
remaining  is  one  thousand  cubic  feet,  and  that  this  quantity 
passes  a  given  point  at  the  foot  of  the  fall  in  half  an  hour, 
we  should  have  a  falling  force  of  one  thousand  cubic  feet 
through  a  space  of  fifty  feet  perpendicular  height,  making 
fifty  thousand  foot-pounds  for  every  half  hour;  and  if  the 
flow  of  the  river  from  waters  derived  from  oilier  rains  upon 
E 


98  FALLING   FOKCE. 

the  mountains  was  continuous,  and  if  all  the  water  flowing 
down  the  cascade  could  be  intercepted  by  a  dam  and  kept 
up  to  a  level  with  the  top  of  the  cascade,  so  as  to  get  the 
whole  falling  force  at  once  through  a  gateway  in  the  dam 
at  the  lower  end  of  the  cascade,  the  "  mill  privilege,"  as 
mill-men  call  such  a  place,  would  be  one  of  one  hundred 
thousand  foot-pounds  an  hour.  It  could  not  be  any  less, 
except  so  far  as  some  portion  of  the  force  might  be  wasted 
by  accidental  impediments  or  by  imperfections  in  the  con- 
structions, and  it  could  not  possibly,  under  any  circum- 
stances, be  more. 

Now  it  is  strictly  on  these  principles  that  all  engineers 
and  millwrights  make  their  calculations  in  estimating  the 
availability  of  any  "  mill  privilege"  as  a  source  of  power. 
It  is  true  that  in  ordinary  cases — that  is,  in  the  building 
of  saw-mills  and  grist-mills  on  streams  of  moderate  size  in 
the  country,  men  do  not  usually  make  any  very  accurate 
measurements,  nor  do  they  express  the  results  of  their  cal- 
culations often  in  numbers,  or  in  any  other  mathematical 
form;  but  they  are  perfectly  familiar  with  the  principle — 
that  is,  they  understand  on  what  two  elements  the  force 
depends,  namely,  on  the  quantity  of  water  that  they  can 
command,  and  on  the  whole  perpendicular  height  from 
which  it  falls  or  by  which  it  presses.  And  in  all  large,  ex- 
pensive, and  important  undertakings,  where  skilled  engi- 
neers are  employed  to  make  the  calculations  and  the  esti- 
mates, the  force  they  have  to  deal  with  is  often  determined 
from  these  elements  with  mathematical  exactness,  the  num- 
ber of  foot-pounds  at  their  command  is  precisely  ascer- 
tained, the  portion  of  this  which  can  not  be  made  availa- 
ble, through  friction  and  waste,  is  allowed  for,  and  no  one 
dreams  of  getting  any  more  work  done  in  the  mill,  by  any 
kind  of  machinery  whatever,  than  can  be  done  by  iising 
the  balance  of  this  force  to  the  best  advantage — none,  I 


POTENTIAL   FORCE.  99 

ought  to  say,  except  such  ill-informed  and  misguided, 
though  often  very  ingenious  inventors,  who  imagine  that 
they  can  sooner  or  later  contrive  not  only  to  make  ma- 
chines, but  also  to  create  the  force  by  which  to  drive  them. 

"  Thus  you  see,"  said  Lawrence,  as  he  walked  along  the 
road  with  John  on  his  return  from  the  woods,  and  after 
making  in  substance  the  preceding  explanation, "  the  ob- 
ject of  a  dam  at  the  foot  of  a  cascade  which  falls  a  certain 
number  of  feet  in  a  certain  distance  is  to  reserve  and  ac- 
cumulate the  whole  of  that  falling  force,  so  as  to  take  it  all 
at  once  out  at  the  gate  in  the  dam.  Thus  the  pond  formed 
by  the  dam  is  essentially  a  reservoir  of  force — that  is,  it  is 
a  reservoir  of  water  only  for  the  sake  of  the  potential  force 
that  is  in  it." 

"Potential,"  repeated  John.  It  was  the  first  time  he 
had  heard  that  word  in  such  a  connection. 

"  Yes,"  rejoined  Lawrence.  "  When  the  gate  is  shut  and 
the  water  in  the  pond  is  still,  it  is  not  exercising  any  actual 
force,  but  it  has  within  it,  so  to  speak,  a  falling  force  often 
feet — if  that  is  the  height  of  the  dam — which  may  be  called 
into  exercise  any  moment  by  opening  a  passage  and  allow- 
ing it  to  fall.  For  every  cubic  foot  of  water  there  would 
be  what  is  called  A  potential  force — that  is,  a  possibility  of 
exercising  an  actual  force  of  ten  foot-pounds  depending 
upon  the  possibility  of  allowing  it  to  fall  ten  feet.  This 
is  called  potential  force,  or,  more  accurately,  potential  en- 
ergy, for,  as  has  already  been  said,  there  are  several  differ- 
ent meanings  to  the  word  force,  and  the  word  energy  de- 
notes this  particular  kind,  and  several  others  that  are  anal- 
ogous to  it — that  is,  all  that  kind  of  force  which  can  trans- 
fer itself  from  one  body  to  another,  and  which  exhausts 
itself  in  one  just  in  proportion  as  it  takes  effect  upon  the 
other." 

"I  don't  understand  it  very  well,"  said  John. 


100 


FALLING   FOKCE. 


"  No,"  said  Lawrence ;  "  all  that  you  can  expect  to  ob- 
tain the  first  time  you  consider  such  a  subject  as  this  is  a 
little  glimmering  of  light,  which  glimmering,  however,  will 
grow  stronger  and  stronger  every  time  you  think,  or  read, 
or  hear  about  it,  and  at  length  your  ideas  will  become  clear 
and  definite.  I  can,  perhaps,  make  the  glimmering  a  little 
brighter  now  by  an  example. 


TJia  MiE-DKlVEB. 


"  The  case  of  tlie  pile-driver  is  as  good  as  any.  Suppose 
the  block  of  iron  to  weigh  five  hundred  pounds,  and  that 
the  height  to  which  it  is  raised  by  the  men  at  the  windlass 
is  twenty  feet.  Now,  to  do  this,  the  men  will  have  exerted 
an  energy  of  ten  thousand  foot-pounds.  This  amount  is 
actually  spent  and  gone  from  their  limbs  and  muscles,  and 
can  never  be  used  by  them  again.  It  is  true  that  they  can 
raise  the  weight  again,  but  it  will  be  by  new  strength,  ac- 


ENERGY.  101 

• 

quired  by  the  digestion  of  a  new  portion  of  food  in  their 
systems,  or,  rather,  by  the  consumption  of  the  results  of 
such  digestion.  That  which  carried  up  the  heavy  weight 
is  expended  and  gone  from  them,  and  has  been  transferred 
to  the  weight  that  has  been  raised  twenty  feet  into  the  air, 
where  it  exists  as  potential  energy  in  the  weight,  and  re- 
mains in  that  condition  as  long  as  the  weight  remains  in 
the  air  twenty  feet  from  the  ground. 

"When  at  length  the  hammer  is  let  fall,"  continued  Law- 
rence, "the  potential  becomes  actual  energy  without  any 
change  in  the  amount  of  it,  or,  rather,  the  potential  is  con- 
verted into  actual  active  energy  by  degrees  as  it  descends. 
At  the  instant  before  it  strikes  the  head  of  the  pile,  the 
whole  of  the  potential  energy  has  been  converted  into  act- 
ive energy,  and  at  the  instant  of  impact  it  is  nearly  all 
transferred  to  the  pile,  heating  the  head  of  it  in  some  de- 
gree, and  driving  it  bodily  into  the  ground.  The  energy 
is  not  destroyed  even  then ;  but  we  can  not  follow  it  any 
farther  now,  for  what  I  wish  to  do  is  to  brighten  a  little 
the  glimmering  of  your  idea  of  the  peculiar  kind  offeree 
which  is  denoted  scientifically  by  the  word  energy." 

"You  have  brightened  it  considerably,"  said  John ;  "but 
what  other  kind  of  force  is  there  ?" 

"  Gravitation  is  sometimes  called  a  force,"  said  Law- 
rence— "that  is,  the  action  of  the  earth  and  the  iron  upon 
each  other  in  drawing  them  together.  This  action,  too,  is 
very  properly  called  a  force,  according  to  the  ordinary  use 
of  language.  But  this  force  does  not  expend  itsclf'm  the 
same  way  and  in  the  same  sense  as  the  force  does  which  is 
generated  in  a  falling  body,  or  in  the  limbs  and  muscles 
of  a  man,  or  that  which  is  developed  by  the  heat  of  the 
fire  under  the  boiler  of  a  steam-engine.  The  cohesion,  too, 
by  which  the  particles  of  a  solid  are  held  together  is  some- 
times called  a  force,  but  that  is  not  a  force  in  the  sense  in 


102  FALLING   FORCE. 

which  the  word  is  used  in  the  case  of  a  falling  body  or  the 
working  of  machinery,  for  this  last  is  a  potency  which,  just 
so  far  as  it  is  exerted,  is  exhausted  in  one  body,  and  brought 
into  action  in  another.  So,  to  recognize  the  distinction, 
scientific  men  sometimes  designate  gravitation,  cohesion, 
and  the  like,  as  properties  of  the  bodies  in  which  they  re- 
side, while  the  other  kind  of  force  is  called  energy,  which 
last  also  may  be  of  two  kinds,  or,  rather,  may  exist  in  two 
forms,  actual  and/xrfefe&oZ." 

John  said,  after  hearing  all  this,  that  his  glimmering  of 
an  idea  had  become  very  much  brightened  by  the  explana- 
tion. Lawrence  told  him,  however,  that  he  must  expect 
to  get  into  confusion  again  a  great  many  times  befofe  his 
ideas  became  clear  in  respect  to  the  subject,  even  so  far  as 
it  was  at  present  understood. 

By  this  time  they  had  come  back  as  far  as  to  the  mill, 
where  they  had  rested  for  a  time  on  their  way  out  to  the 
wood.  They  stopped  a  moment  at  the  roadway  leading 
up  to  the  mill,  seen  on  the  left  of  the  picture  in  the  last 
chapter,  and  stood  there  a  few  moments  looking  at  the 
pond  which  had  been  formed  by  the  dam. 

"  One  would  say,  in  looking  at  it,"  said  Lawrence,  "  that 
it  was  a  reservoir  of  water  ;  but  it  is  more  strictly  a  reser- 
voir of 'force — that  is,  that  portion  of  the  falling  force  which 
is  kept  in  a  potential  form  by  the  water  being  held  up  to 
a  higher  level,  and  so  not  allowed  to  fall ;  that  is  to  say,  is 
not  allowed  to  convert  that  portion  of  potential  energy 
represented  by  the  height  of  the  dam  into  actual  energy, 
excepting  as  fast  as  the  mill-men  are  prepared  to  use  it." 

"  Thus  you  see,"  continued  Lawrence,  "  that  a  dam  may 
be  made  to  hold  back,  or,  rather,  to  hold  up  the  water  of 
the  river  for  two  distinct  purposes — that  is,  it  may  be  for 
the  sake  of  the  water  or  for  the  sake  of  the  force.  The 
dam  upon  the  Croton  River  in  New  York,  for  example,  is 


RICK    REAPPEARS. 


103 


THE   MILL-POND. 


for  the  purpose  of  retaining  the  water,  while  that  at  Law- 
rence or  Lowell  is  for  retaining  the  force.  At  Lawrence 
and  Lowell  they  intercept  and  use  the  force,  and  let  the 
water  flow  away  down  the  stream,  except  so  far  as  they 
may  wish  to  take  off  a  small  portion  of  it  to  use  in  their 
houses.  At  Groton,  on  the  other  hand,  they  intercept  the 
water,  and  let  the  force  flow  away,  except  so  far  as  they 
wish  to  use  a  small  portion  of  it  to  carry  the  water  into 
the  upper  stories  of  houses,  or  to  form  jets  and  fountains 
in  the  parks." 

Just  at  this  point  John  moved  his  head  toward  Law- 
rence's ear,  and  said,  in  a  mysterious,  half  whispering  voice, 
"Look  in  that  clump  of  bushes  close  to  the  water  on  the 
right.  There's  Rick !  He  is  hiding.  He's  afraid  you  will 
give  him  a  scolding  for  running  away,  and  I  would  give 
him  one  if  I  were  you." 


104  FALLING   FOKCE.  ' 

"  No,  indeed,"  said  Lawrence.  And  then,  pretending  not 
to  observe  that  Kick  was  trying  to  hide,  he  called  out  in 
his  usual  tone  of  voice,  holding  up  at  the  same  time  one 
of  his  pieces  of  wood, "  Rick,  come  here  and  see  our  bat 
sticks,  and  tell  me  if  you  think  they  will  do." 

So  Rick,  finding  himself  discovered,  came  somewhat  awk- 
wardly out  of  his  hiding-place,  and  walked  toward  the  place 
where  Lawrence  and  John  were  standing.  Lawrence  show- 
ed him  the  wood,  and  Rick  examined  all  the  pieces  with 
great  attention.  He  thought  they  would  do  very  well. 
He  then  began  to  apologize  for  running  away,  but  Law- 
rence told  him  it  was  of  no  consequence. 

"  You  came  with  us  and  helped  us  find  the  wood,"  said 
he,  "  and  you  are  entitled  to  your  share  of  the  bats." 

"  Or,  if  you  like,"  continued  Lawrence, "  you  can  do  a 
little  more  than  your  share  of  the  turning,  as  we  did  a  lit- 
tle more  than  our  share  of  the  cutting." 

Rick  said  that  he  should  like  to  do  that  very  much,  and 
from  that  time  seemed  entirely  at  his  ease.  Lawrence 
made  no  allusion  to  his  running  away  except  to  say, "  I 
see  you  did  not  kill  the  squirrel.  I'm  sorry,  for  I  would 
have  helped  you  tan  the  skin  if  you  had  caught  him." 

Rick  said  he  believed  he  should  have  caught  him,  but  he 
disappeared  in  a  very  tall  tree.  He  believed  he  ran  into 
a  hole  there.  He  said,  moreover,  that  he  tried  to  go  back 
to  the  place  where  they  were  cutting  the  hornbeam,  but 
that  he  could  not  find  his  way.  Lawrence  said  that  it  was 
no  matter;  he  could  easily  make  it  up  by  doing  a  little 
more  work  in  the  turning. 

Then  they  set  out  again  on  their  walk.  Lawrence  said 
he  was  going  to  examine  John  in  respect  to  some  princi- 
ples in  respect  to  force  that  he  had  been  explaining  to  him. 
He  was  going  to  examine  him,  he  said,  about  the  philoso- 
phy of  sliding  down  hill,  01*,  as  he  called  it,  coasting. 


SLIDING   DOWN   HILL.  105 

"  But  you  did  not  tell  me  about  coasting,"  said  John. 

"  No,"  replied  Lawrence,  "  but  I  explained  to  you  prin- 
ciples that  apply  to  coasting,  and,  if  you  understand  the 
principles,  you  can  make  a  new  application  of  them  youi'- 
self.  Let  us  suppose  that  there  is  a  boy  with  his  sled  on 
the  top  of  a  hill.  How  much  shall  we  suppose  the  boy  to 
weigh  ?" 

"I  can  tell  you  what  I  weigh  exactly,"  said  Rick,  "  for  I 
was  weighed  the  other  day ;  it  was  seventy — something." 

Lawrence  half  smiled  at  this  answer,  saying  to  himself 
that  Rick  had  a  long  road  to  travel  in  respect  to  his  ideas 
of  exactness  before  he  would  be  able  to  appreciate  the  dif- 
ference between  the  lengths  of  the  waves  in  a  red  and  in  a 
violet  ray  of  light. 

"Very  well,"  said  he.  "Let  us  suppose  that  the  boy 
weighs  seventy-five  pounds  and  the  sled  twenty-five;  that 
makes  one  hundred  pounds.  Now,  how  high  shall  we  sup- 
pose the  hill  to  be  ?" 

"  Half  a  mile,"  said  Rick,  promptly,  encouraged  by  find- 
ing that  his  estimates  were  received  and  adopted. 

"  Yes,"  said  Lawrence, "  half  a  mile ;  that  would  be  just 
right  for  a  good  slide.  Now,  suppose  there  was  a  church 
on  the  level  ground  at  the  foot  of  the  hill,  and  it  had  a 
tower  fifty  feet  high,  and  that  the  top  of  the  hill  was  just 
level  with  the  top  of  the  tower :  that  would  make  the  hill 
fifty  feet  high  perpendicular." 

Rick  looked  a  little  puzzled. 

"Or  suppose,"  continued  Lawrence,  "a  well  was  to  be 
dug  at  the  top  of  the  hill  where  the  boy  was  beginning  to 
slide,  and  made  so  deep  that  the  bottom  of  it  was  just  level 
with  the  bottom  of  the  hill ;  then  the  depth  of  the  well, 
which  would  show  the  perpendicular  height  of  the  hill, 
would  be  fifty  feet." 

Rick  now  began  to  understand  what  was  meant  by  the 
E2 


106 


FALLING   FORCE. 


perpendicular  height  of  a  hill,  and  Lawrence  was  going  on 
to  explain  that  as  the  boy  and  the  sled  weighed  one  hun- 
dred pounds,  and  the  height  of  the  hill  was  fifty  feet,  the 
whole  force  at  command  for  carrying  the  boy  down  the 
hill,  and  shooting  him  forward  a  certain  distance  on  the 
level  ground  at  the  bottom  of  it,  would  be  the  falling  force 
of  one  hundred  pounds  descending  through  a  space  of  fifty 
feet,  which  would  make  exactly  five  thousand  foot-pounds, 
and  this  force  would  all  be  expended  in  the  friction  of  the 
runners  on  the  snow,  and  the  resistance  of  the  air  to  the 
passing  of  the  boy  and  the  sled  through  it.  But,  finding 
that  Kick  began  to  look  a  little  inattentive,  and  also,  at  the 
same  time,  coming  in  sight  of  a  somewhat  curiously-built 
bridge,  which  was  built,  in  fact,  somewhat  on  the  plan  of 
the  one  shown  in  this  engraving,  he  determined  to  change 
the  conversation. 


A   KING-POST. 


THE    KING-POST.  107 

"  Look  at  that  bridge,"  said  he, "  and  at  the  cm-ions  kind 
of  railing  there  is  built  over  it.  Let  us  see  which  of  you 
will  come  nearest  to  guessing  what  that  railing  is  for." 

"It  is  for  a  guard  to  keep  the  teams  from  driving  off 
into  the  water,"  said  Rick. 

"  No,"  said  John ;  "  those  frames  are  not  shaped  right  for 
that ;  they  must  be  for  ornament — that  is,  to  put  a  finish 
upon  the  bridge,  and  make  it  look  better." 

"  I  think  that  Rick  has  come  rather  the  nearest,"  said 
Lawrence, "for  they  are  for  utility  rather  than  for  orna- 
ment, and  his  guess  was  for  a  kind  of  utility.  They  are 
really  to  support  the  bridge — that  is,  they  are  made  to  hold 
up  the  middle  of  the  beams  by  hanging  the  middle  por- 
tion, as  it  were,  to  the  two  ends.  You  see  the  two  ends 
are  held  up  by  the  stone  piers,  and  the  middle  is  prevented 
from  sagging  by  the  two  braces  which  come  together  in 
the  middle  above,  and  by  a  post  hanging  down  from  the 
ridge  where  they  join,  and  holding  up  the  middle  of  the 
beam  by  an  iron  strap  going  round  it." 

"  Ah,  yes,"  said  John  ;  "  I  see  it." 

"  Such  a  post  as  this,"  added  Lawrence, "  which  holds  up 
the  middle  of  a  beam  by  suspending  it  from  two  rafters 
braced  against  each  other  above,  is  called  a  king-post." 

If  John  had  been  a  mere  boy,  he  would  have  said,  "I 
don't  think  Rick's  guess  was  any  better  than  mine."  But 
he  had  by  this  time  attained  to  manliness  of  character 
enough  to  be  willing  that  Rick  should  have  the  credit  of 
making  the  best  guess.  He  knew  very  well  that  giving 
him  this  credit  would  tend  to  encourage  him,  and  help 
Lawrence  forward  in  the  experiment  which  he  was  making 
upon  him. 

And  so  they  went  homo. 


108  HEAT. 


CHAPTER 


IT  must  be  understood  at  the  outset  that  the  word  heat, 
in  its  scientific  sense,  does  not  relate  exclusively  to  that 
state  of  the  temperature  in  any  substance  which  produces 
the  feeling  of  heat  to  the  hand,  but  to  that  which  causes  all 
differences  of  temperature  whatever.  Thus,  if  a  piece  of 
ice  is  brought  in  from  out  of  doors  when  the  thermometer 
is  ten  degrees  below  zero,  into  a  cold  room  where  it  is  only 
two  below  freezing,  its  temperature  will  be  raised  from  ten 
below  to  thirty  above  zero — that  is,  it  will  be  raised  forty 
degrees.  Scientific  men  say  in  such  a  case  that  the  ice  has 
received  an  accession  of  heat,  although  to  the  hand  it  will 
still  feel  intensely  cold.  In  this  sense  there  is  no  known 
substance  that  is  entirely  destitute  of  heat.  Such  a  state 
of  things  is,  however,  conceivable.  Indeed,  the  zero  of  our 
thermometers  was  once  supposed  to  mark  complete  and 
absolute  destitution  of  heat.  It  was  soon  found,  however, 
that  that  point  was  not  reached  by  any  degree  of  cold 
within  our  experience.  The  point  which  in  theory  corre- 
sponds with  perfect  destitution  of  heat  is  called  the  abso- 
lute zero,  and  many  experiments  and  calculations  have  been 
made  to  determine  where  it  would  come  in  relation  to  the 
degrees  marked  on  our  thermometers.  The  result  of  these 
calculations,  which  are  too  intricate  and  complicated  to  be 
here  explained,  is  that  absolute  cold — that  is,  a  perfect  ab- 
sence of  that  quality  in  bodies  which  produces  the  phenom- 
ena of  heat,  would  correspond,  if  it  were  possible  to  meas- 


DEGREES   OF   COLD.  109 

urc  and  mark  it  by  a  thermometer,  with  490°  below  the 
zero  of  Fahrenheit. 

It  would,  however,  not  be  possible  to  measure  it,  or, 
rather,  to  denote  it  by  any  thermometer.  Mercury,  which 
is  the  substance  with  which  most  thermometers  are  filled, 
freezes  at  forty  below  Fahrenheit's  zero,  and,  of  course,  can 
not  mark  any  temperature  colder  than  that.  Alcohol  re- 
mains fluid  at  a  much  lower  point,  and  is  always  used  in 
arctic  and  other  regions  where  the  cold  goes  below  the 
freezing  point  of  mercury.  But  even  alcohol  would  fail 
long  before  the  above  zero  would  be  reached,  for  Faraday, 
by  means  of  a  certain  chemical  process,  produced  a  cold 
of  220°  below  Fahrenheit's  zero,  and  at  that  temperature 
the  alcohol  became  thickened  like  a  sirup,  and  would  un- 
doubtedly have  become  solid  long  before  reaching  the  ab- 
solute zero  270°  below. 

The  greatest  cold  experienced  in  any  part  of  the  United 
States  is  about  the  freezing  point  of  mercury — that  is, 
about  forty  degrees  below  the  zero  of  Fahrenheit.  In  the 
arctic  regions  a  cold  of  about  eighty  degrees  has  been  ob- 
served by  explorers.  At  about  —220°  or  —230°  alcohol 
probably  freezes,  and  the  utter  privation  of  all  heat — that 
is,  the  absolute  zero — is  now  generally  supposed  by  scien- 
tific men  to  be  at  —490°.  It  is  well  for  the  young  student 
to  fix  these  numbers  in  his  mind. 

Until  within  quite  recent  times  the  cause  of  the  phenom- 
ena of  heat  has  been  considered  to  be  a  peculiar  and  very 
subtle  substance  which  was  called  caloric.  It  is  now,  how- 
ever, universally  believed  that  there  is  no  such  specific  sub- 
stance, but  that  heat  is  one  of  the  forms  which  force  as- 
sumes in  the  interactions  of  atoms  and  molecules  upon  each 
other,  and  the  term  caloric  has  gone  entirely  out  of  use 
among  scientific  men.  This  interaction  is  supposed  to  be 
of  the  nature  of  an  intense  quivering — or,  as  one  writer 


110  HEAT 

calls  it,  shivering — vibration  of  the  particles  among  each 
other,  though  this  word  shivering  seems  to  be  a  singular 
term  to  apply  to  heat  in  any  sense.  We  can  not,  however, 
probably  depend  upon  the  accuracy,  or,  rather,  the  ade- 
quacy of  any  definite  notions  that  we  can  form  of  the  ex- 
act nature  and  character  of  an  action  so  far  removed  from 
the  cognizance  of  our  senses;  but  there  can  be  no  doubt 
that  heat,  in  all  the  degrees  of  it,  is  really  one  of  the  forms 
which  force  assumes  when  it  passes  from  the  mechanical 
movement  of  masses  into  the  interior  substance  of  which 
the  masses  are  composed. 

Perhaps  the  most  obvious  example  of  this  transforma- 
tion is  the  case  of  friction,  the  mechanical  force  with  which 
a  body  is  rubbed  giving  rise  to  heat  in  the  rubbed  sub- 
stance in  proportion  as  the  mechanical  force  disappears. 
This  effect  has,  of  course,  always  been  known,  but  it  was 
formerly  thought  that  the  mechanical  force  in  some  way 
disturbed  and  brought  out  the  "  caloric,"  as  it  was  called, 
which  caloric  previously  existed,  in  some  secret  form,  in  the 
substance  rubbed.  That  great  heat  can  be  produced  in 
this  way  was  known  from  the  earliest  times.  Indeed,  sav- 
age nations  in  all  parts  of  the  world  have  been  accustomed 
to  procure  fire  in  this  way,  though  civilized  men  have  found 
it  very  difficult  to  imitate  their  example.  It  required,  no 
doubt,  some  special  kinds  of  wood,  having  the  requisite 
qualities  of  hardness  and  combustibility,  which  only  the 
savages  themselves  knew  how  to  find.  There  are  many 
representations  of  the  manner  in  which  the  operation  was 
performed  among  different  tribes.  Sometimes  they  made 
use  of  a  bow — on  the  principle  described  in  a  former  chap- 
ter as  used  in  the  bow-lathe — for  producing  rapid  rotation. 

It  is  not  thought  probable  that  savages  could  actually 
set  the  wood  itself  on  fire  by  means  of  any  force  that  they 
could  apply  in  this  way,  but  only  that  they  could  produce 


FORCE   TAKING   THE   FORM   OF   HEAT. 


Ill 


FIEE  BY   FRICTION. 


such  a  degree  of  heat  that  they  could  inflame  by  it  some 
kind  of  very  light  and  decayed  wood,  or  pith  perhaps,  or 
some  other  substance  which  they  had  learned  to  employ  as 
tinder. 

And  yet  it  is  not  uncommon  for  machinery  at  the  pres- 
ent day — the  wheels  of  cars  in  a  railroad  train,  for  exam- 
ple— to  develop  so  much  heat,  if  the  bearing  parts  are  not 
properly  polished,  or  are  not  kept  thoroughly  lubricated, 
as  to  inflame  the  wood  that  is  near  them. 

Savages  always  attribute  all  those  phenomena  which 
take  place  around  them,  which  they  can  not  understand 
and  can  not  effect  themselves,  to  the  agency  of  spirits,  good 
or  bad,  and  there  are  many  traces  among  various  nations 
of  their  entertaining  such  ideas  in  connection  with  the  won- 
derful mysteries  of  fire,  and  of  their  connecting  the  pro- 
duction of  fire  in  various  ways  with  their  religious  rites 
and  observances.  The  following  engraving  is  copied  from 


112 


HEAT. 


a  sculpture  found  in  Mexico,  and  evidently  gives,  in  a  high- 
ly idealized  or  symbolic  form,  a  representation  not  only  of 
fire  itself,  but  of  the  act  of  a  priest  in  obtaining  it  by  fric- 
tion while  dressed  in  his  sacerdotal  vestments,  and  kneel- 
ing, as  if  the  operation  was  part  of  a  religious  ceremony. 


Although  many  animals  show  so  much  intelligence,  in 
certain  respects,  in  counterfeiting  the  action  of  men,  none 
seem  to  be  capable  of  doing  any  thing  with  fire.  Many  of 
them — as  our  cats  and  dogs,  for  instance — appear  greatly 
to  enjoy  the  comfort,  and  perhaps  even  the  sense  of  com- 
panionship which  a  fire  affords  them,  but  I  believe  that  no 
dog  ever  conceived  the  idea  of  bringing  even  the  smallest 
stick  of  wood  to  replenish  the  fire  by  which  he  was  lying 
when  he  began  to  feel  cold  from  its  going  down.  There 
are  some  dogs  that  might  possibly  be  taught  to  do  this, 
but  most  housekeepers  would  probably  think  it  would  be 
rather  a  dangerous  accomplishment  for  such  an  animal  to 
acquire. 

It  is  said  that  some  races  of  monkeys  are  very  much  at- 


FIRE    FROM   FRICTION.  113 

tracted  by  the  remains  of  the  fires  which  travelers  some- 
times leave  glowing  upon  the  ground  at  their  encamp- 
ments when  they  go  forward  on  their  journey,  and  that 
they  assemble  and  gambol  around  them  with  great  delight; 
but,  though  they  have  sense  enough  to  gather  sticks  for 
weapons  that  they  may  throw  them  at  their  enemies,  they 
never,  it  seems,  conceive  the  idea  of  using  them  as  fuel  to 
keep  up  the  fire  in  the  deserted  encampment  after  the  party 
of  travelers  have  gone  away  and  left  them  in  possession  of  it. 

And  yet  the  very  lowest  savages  are  familiar  with  the 
use  of  fire,  and  some  writers  have  formed  ingenious  specu- 
lations on  the  possible  modes  by  which  this  wonderful 
agency  may  have  been  first  made  known  to  them,  before 
they  were  advanced  enough  to  produce  it  themselves  by 
friction.  The  conceivable  modes  by  which  fire  may  be 
supposed  to  have  been  produced  for  them  by  natural  means 
are  four,  namely  :  1st.  The  accidental  collision  of  one  stone 
with  another  may  possibly,  in  some  very  rare  combination 
of  circumstances,  have  set  dried  grass  or  leaves  on  fire ; 
2d.  Lightning,  in  striking  a  tree  in  the  woods,  may  have 
enkindled  a  flame ;  3d.  It  is  barely  possible  that  one  branch 
of  a  tree  in  the  forest  may  have  been  rubbed  against  an- 
other by  the  action  of  the  wind  in  a  violent  gale,  and  in  a 
very  dry  time,  with  such  force  as  to  develop  heat  enough 
to  produce  combustion  ;  and,  4th.  The  fire  may  have  been 
furnished  by  the  heat  of  the  molten  lava  coming  down  the 
sides  of  a  volcano  into  the  forests  below. 

But  by  whatever  accidental  mode  we  may  suppose  that 
the  primeval  man,  in  emerging  from  the  mere  animal,  and 
entering  into  a  more  properly  human  condition,  may  have 
first  made  the  discovery  of  the  nature  and  action  of  fire, 
there  is  no  doubt  that  practically  the  ordinary  method 
adopted  among  all  savage  nations  for  procuring  fire  in 
the  primeval  ages  was  the  friction  of  wood;  and,  curiously 


114  HEAT. 

enough,  after  so  long  a  time,  and  in  the  highest  state  of 
civilization  yet  attained,  we  have  all  returned  to  the  same 
primitive  method.  For  the  universal  practice  at  the  pres- 
ent day  for  procuring  fire  is  by  the  friction  of  wood,  only 
we  have  contrived  to  envelop  the  portion  of  wood  subject- 
ed to  the  friction,  in  order  to  aid  in  commencing  the  pro- 
cess of  combustion,  with  a  substance  that  is  more  readily 
inflamed  than  the  dried  pith,  or  fungus,  or  punk  employed 
by  the  savages. 

Heat  being  not  any  specific  substance,  but  only  a  form 
which  force  assumes  when  it  passes  from  the  motion  of 
masses  as  wholes  to  that  of  the  atoms  and  molecules  of 
which  the  masses  are  composed,  it  was  to  be  expected — 
in  accordance  with  the  principle  advanced  in  a  previous 
chapter,  namely,  that  no  force  can  be  either  increased  or 
diminished  in  amount,  but  can  only  undergo  transmutation 
of  form — that  the  quantity  of  heat  which  can  be  developed 
by  a  given  amount  of  mechanical  force  would  be  fixed  and 
determinate;  and  this  has  been  found  to  be  in  all  cases 
strictly  true.  The  expenditure  of  a  certain  amount  of  en- 
ergy will  produce  a  certain  definite  amount  of  heat,  neither 
less  nor  more;  and  a  certain  definite  amount  of  heat  will 
do  a  certain  precise  amount  of  work,  neither  less  nor  more. 
By  work,  however,  as  the  term  is  used  scientifically,  is 
meant  not  exclusively  useful  effect,  but  effects  of  all  kinds, 
including  the  overcoming  the  resistance  of  the  air  and  the 
friction  arising  from  the  imperfection  of  machinery.  This 
is  all  work,  in  the  scientific  sense,  that  the  heat  has  to  do, 
and  it  has  been  found,  by  a  great  variety  of  experiments 
and  observations,  made  by  many  different  investigators  in 
many  different  countries,  that  the  quantity  of  heat  and  the 
quantity  of  mechanical  motion  which  may  be  converted 
Into  each  other  have  a  fixed  and  determinate  ratio,  from 
which  there  is  never  any  possible  deviation.  This  ratio  is 


MODE    OF   MEASURING    HEAT.  115 

expressed  by  a  certain  formula  which  denotes  what  is 
termed  the  mechanical  equivalent  of  heat,  and  which  every 
young  man  interested  in  the  study  of  science  ought  to  fix 
in  his  memory.  It  is  this: 

1  unit  of  heat  =  772  foot-pounds. 

But  what  is  a  unit  of  heat?  What  a  foot-pound  is  has 
already  been  explained,  namely,  that  amount  of  force  which 
is  generated  by  gravitation  acting  upon  one  pound  during 
its  descent  through  a  space  of  one  foot;  and  772  foot- 
pounds would  be  the  force  imparted  to  a  similar  body  in 
descending  through  a  space  of  772  feet,  or  a  body  weigh- 
ing 772  pounds  descending  through  a  space  of  one  foot,  or 
one  of  any  other  weight  descending  through  a  space  in  the 
same  inverse  proportion. 

Some  persons  are  at  first  inclined  to  imagine  that  the 
force  imparted  to  a  body  in  the  lower  portions  of  the  space 
through  which  it  descends  is  greater  than  that  which  is  im- 
parted at  the  commencement  of  it,  from  the  fact  that  its 
motion  becomes  so  much  swifter,  and  the  force  with  which 
it  strikes  is  so  much  greater  toward  the  close  of  its  descent. 
But  this  increase  of  velocity  and  force  is  due  to  the  accu- 
mulation of  all  the  different  additions  offeree  to  it  in  all 
the  different  portions  of  its  descent,  and  not  to  any  increase 
in  the  force  imparted  to  it  in  the  lower  portions.  There  is 
a  very  slight  difference,  it  is  true,  owing  to  the  differing 
distances  of  the  body  from  the  centre  of  the  earth,  but  this 
difference  is  wholly  inappreciable.  Practically  the  amount 
of  force  imparted  by  gravitation  is  the  same  for  every 
pound  and  for  every  distance  within  reasonable  limits,  so 
that  the  force  represented  by  a  descent  of  772  pounds 
through  one  foot  is  the  same  with  that  of  one  pound 
through  772  feet,  and  so  in  all  other  cases. 

But  what  is  a  unit  of  heat  ?  In  all  cases  of  the  meas- 
urement of  quantities  of  whatever  kind,  it  is  necessary  to 


116  HEAT. 

take  some  portion  of  the  quantity  to  be  measured  as  the 
unit)  as  it  is  called.  Thus  the  foot  is  a  unit  of  measure- 
ment for  linear  space,  and  an  hour  for  time.  The  English 
unit  of  measurement  for  heat  is  the  quantity  of  heat  which 
is  necessary  to  raise  the  temperature  of  one  pound  of  water 
one  degree  of  Fahrenheit's  thermometer — that  is,  suppose 
we  have  a  kettle  containing  one  pound  of  water ;  we  as- 
certain its  temperature ;  we  then  build  a  fire  under  it  and 
wait  until  the  water  is  warmed  one  degree.  Now,  the  quan- 
tity of  heat  which  has  passed  up  through  the  iron  of  the 
kettle,  and  entered  into  the  water,  and  has  been  expended 
in  raising  the  temperature  one  degree,  is  taken  for  the  unit 
of  heat. 

"I  do  not  see  how  they  can  tell  precisely  how  much 
goes  in,"  said  John,  one  day,  when  Lawrence  was  explain- 
ing this  to  him. 

"  They  can  not  tell  exactly  in  such  a  case  as  this,"  said 
Lawrence, "  for  a  great  deal  of  the  heat  made  by  the  fire 
would  pass  around  by  the  sides  of  the  kettle  up  the  chim- 
ney ;  and  it  would  be  impossible,  too,  to  stop  the  experi- 
ment at  the  precise  instant  when  the  whole  of  the  water 
would  be  warmed  exactly  one  degree.  Still,  that  quantity, 
whatever  it  is,  and  however  we  might  attempt  to  insulate 
and  determine  it,  is  taken  as  the  standard.  There  are 
modes,  moreover,  by  which  that  exact  amount  may  be  in- 
sulated and  made  subject  to  experiment.  Such  a  quantity 
forms  what  is  called  the  unit  of  heat,  and  it  is  found  that 
this  amount  of  heat  is  precisely  equivalent  to  772  foot- 
pounds offeree — that  is  to  say,  the  fall  of  one  pound  weight 
through  a  space  of  772  feet,  or  of  772  pounds  through  one 
foot,  or  of  one  half  of  772  through  two  feet,  will  develop  ex- 
actly one  unit  of  heat* — that  is,  heat  enough  to  raise  the 

*  The  manner  in  which  this  relation  was  ascertained  by  Joule,  who  was 
one  of  the  first  to  determine  it,  is  explained  in  the  volume  of  this  series  en- 


UP   AND   DOWN.  117 

temperature  of  one  pound  of  water  one  degree  on  its  being 
suddenly  stopped  by  collision  with  a  solid  stibstance. 

The  young  student — and  this  is,  indeed,  often  the  case 
with  many  older  ones — finds  it  difficult  to  picture  to  his 
imagination  what  the  nature  of  the  process  is  by  which 
mechanical  force  is  converted  into  heat  in  passing  from  the 
mass  to  the  interior  constitution  of  the  substance  on  which 
the  mass  impinges.  This  difficulty  can  not  be  entirely 
overcome,  but  there  are  some  considerations  which  carry 
us  a  little  way  in  our  attempt  to  gain  a  comprehension  of 
it ;  and  the  first  step  is  to  form  a  clear  idea  of  what  is, 
philosophically,  the  import  of  the  terms  up  and  down. 

These  terms  do  not,  then,  as  we  are  apt,  without  reflec- 
tion, to  suppose,  refer  to  any  absolute  direction  in  space,  for 
we  all  know  that  on  the  opposite  sides  of  the  earth  the  ab- 
solute directions  are  reversed.  Indeed,  the  absolute  direc- 
tion indicated  by  the  word  downward  is  different  at  every 
different  point  on  the  earth's  surface. 

On  the  same  principle,  down,  in  respect  to  the  sun,  is 
toward  the  sun,  on  every  side — that  is,  in  the  direction  of 
Ms  attraction;  and  in  the  same  manner,  within  the  pre- 
dominating influence  of  the  moon,  down  is  in  the  direction 
of  her  gravitation. 

Thus  the  terms  up  and  down,  in  relation  to  any  centre 
or  point  of  attraction,  denote  respectively  in  opposition  to, 
or  coincidence  with,  the  attraction. 

Now  there  is  something  in  a  certain  degree  analogous 
to  this  in  the  internal  constitution  of  matter — something 
which  might  be  called  the  up  and  down  in  chemistry — that 
is,  there  is  a  certain  state  or  condition  of  the  particles  when 
they  are  quiescent  and  in  repose,  as  a  heavy  body  is  when 
it  is  lying  at  rest  upon  the  ground ;  and  there  is  another 

titled  Heat.  The  formula— 1  unit  of  heat=772  foot-pounds—is  called 
Joule's  equivalent. 


1 1  8  HEAT. 

state  or  condition — which  may  be  produced  by  the  applica- 
tion of  a  sufficient  degree  of  force — when  the  particles  are 
not  in  this  condition  of  repose,  but  have  a  strong  disposi- 
tion or  tendency  to  return  to  it,  like  the  heavy  weight 
above  referred  to,  when  raised  above  the  surface  of  the 
earth  and  sustained  there,  ready,  the  moment  it  is  released, 
to  return  again  to  the  ground  with  the  precise  degree  of 
force  which  was  expended  in  raising  it. 

Whether  these  two  conditions  of  the  particles  of  matter 
depend  upon  the  distance  between  them — that  is,  whether 
the  force  that  is  applied  is  expended  in  separating  the  par- 
ticles from  each  other,  and  the  force  which  they  afterward 
generate  comes  from  their  tendency  to  come  together 
again,  or  whether  the  effects  are  due  to  some  other  modes 
and  operations  of  force  inconceivable  to  us,  may  perhaps 
be  uncertain.  The  general  idea,  however,  now  prevailing, 
is  that  the  mechanical  force  which  expends  itself  in  friction 
or  collision  communicates  its  motion  to  the  particles  of  the 
bodies  concerned  in  such  a  way  as  to  convert  the  motion 
of  the  mass  into  that  motion  of  the  molecules  which  con- 
stitutes heat,  and  that  this  molecular  motion  has  in  some 
mysterious  way  the  effect  of  separating  the  particles  from 
each  other,  or  altering  their  relation  to  each  other  in  some 
other  respect,  so  as  to  leave  them  somewhat  in  the  condi- 
tion of  the  heavy  body  raised  from  the  surface  of  the  earth, 
and  held  there  in  suspense,  with  a  great  tendency  to  fall ; 
and  that,  just  as  when  a  body  so  placed  is  released  and  al- 
lowed to  fall,  it  gives  back  again  in  the  falling  force  pre- 
cisely the  same  amount  of  energy  that  was  expended  in 
raising  it,  so  the  atoms  or  molecules  of  any  substance,  when 
their  position — or,  perhaps,  their  relation  to  each  other  in 
some  other  respect— is  forcibly  altered  by  the  agency,  for 
example,  of  heat,  when  they  are  released  from  their  unnat- 
ural condition  and  allowed  to  return  to  their  normal  ar- 


FALLING   TOGETHER   OF   ATOMS.  119 

rangement,  give  out  precisely  the  same  amount  of  heat 
that  was  expended  in  producing  the  disarrangement,  what- 
ever the  nature  of  the  disarrangement  may  be. 

Take,  for  example,  the  case  of  water.  It  is  composed  of 
oxygen  and  hydrogen  in  a  state  of  intimate  and  compara- 
tively quiescent  union.  By  applying  a  certain  amount  of 
force,  which  may  be  done  by  means  of  heat  or  electricity, 
and,  in  fact,  in  many  other  ways,  this  union  may  be  dis- 
solved, and  the  parts  separated  from  each  other.  They 
have,  however,  an  immensely  strong  tendency  to  come  to- 
gether again,  and  re-form  the  water  from  which  they  were 
derived ;  but  while  they  continue  cold,  they  are,  in  some 
mysterious  way,  kept  from  coming  together  again,  just  as 
the  weight  in  the  pile-driver  is  kept  from  falling  by  some 
kind  of  catch  above.  However  intimately  the  two  gases 
may  be  mingled,  so  long  as  they  remain  cool  they  are  kept 
back  from  combining  ;  but  whenever  even  the  slightest 
portion  of  the  mixture  is  heated  up  to  a  certain  point,  the 
atoms  come  together  with  great  force — with  the  same  force 
exactly  as  that  which  was  expended  in  separating  them — 
and  in  the  collision,  if  collision  it  be,  this  force,  which  is 
extinguished  in  that  form,  becomes  converted  into  that  pe- 
culiar kind  of  motion  which  is  supposed  to  constitute  heat. 

It  is  the  same  substantially  with  all  other  decomposi- 
tions and  rccompositions.  A  certain  amount  of  force  in 
the  form  of  heat  is  required  to  sunder  the  elementary  atoms 
from  each  other.  This  is  called  the  heat  of  dissociation — 
that  is,  the  heat  required  for  the  dissociation  of  the  ele- 
mentary substances  in  any  compounded  body  from  each 
other,  just  as"  the  heat  necessary  to  melt  a  substance  is  call- 
ed the  heat  of  liquefaction,  and  that  of  converting  a  liquid 
into  a  vapor  is  called  the  heat  of  vaporization.  Thus  a 
certain  quantity  of  heat— that  is,  a  certain  number  of  units 
— is  necessary  to  convert  ice  into  water.  The  number  of 


120  HEAT. 

units  required  for  this  purpose  for  every  pound  of  ice  is 
found  to  be  142 ;  that  is,  it  takes  as  much  heat  to  convert 
one  pound  of  ice  to  water  as  would  suffice  to  make  water 
that  was  as  cold  as  ice  142  degrees  warmer;  and  yet  the 
ice,  after  absorbing  all  this  heat,  will  only  be  turned  into 
water,  but  the  water  will  be  as  cold  to  the  hand,  or  to  the 
thermometer,  as  the  ice  was  before.*  Then,  when  the  wa- 
ter comes  to  the  boiling  point,  it  will  take  in  and  conceal, 
as  it  were,  within  its  substance,  about  962  units  of  heat, 
while  yet  the  steam  thus  produced  will  be  no  hotter  than 
the  water  was  when  it  first  began  to  boil.f  This  amount 
of  962  units  constitutes  thus  the  heat  of  vaporization. 
Then,  finally,  when  we  come  to  dissociate  the  oxygen  from 
the  hydrogen — that  is,  to  separate  the  substance  of  the  wa- 
ter itself  into  its  constituent  elements,  an  enormous  quan- 
tity of  heat  will  be  required  —  not  less,  as  some  writers 
state,  than  17,000  units  for  the  pound.  This  is  the  heat  of 
dissociation. 

And  now,  in  reversing  the  process,  when  the  elements 
of  oxygen  and  hydrogen  are  released  from  the  mysterious 
restraint,  whatever  the  nature  of  it  may  be,  that  holds  them 

*  Different  observers  have  come  to  somewhat  different  results  in  de- 
termining the  number  of  units  of  heat  expended  in  the  liquefaction,  and 
also  in  the  vaporization  of  water,  though  these  differences  are  slight,  and 
are  no  greater  than  would  naturally  be  expected  from  slight  and  unavoid- 
able differences  in  the  circumstances  under  which  the  experiments  were 
made.  Sometimes,  however,  English  writers  use  the  notation  of  the  Cen- 
tigrade thermometer  instead  of  that  of  Fahrenheit,  which  makes  a  great 
difference  in  the  numerical  statement  of  the  results,  the  heat  of  liquefac- 
tion being  in  that  case  represented  as  about  79  instead  of  142,  as  stated 
above. 

t  The  number  of  units  of  heat  absorbed  in  making  steam  is  often  reck- 
oned in  round  numbers  as  1000.  Indeed,  the  quantity  is  not  constant, 
varying  as  it  does  somewhat  with  the  degree  of  pressure  under  which  the 
steam  is  produced,  and  the  consequent  temperature  at  which  the  change 
takes  place. 


RESTORATION    OF   HEAT.  121 

apart  while  they  are  cold,  and  allows  them  to  come  togeth- 
er again  to  form  the  water  from  which  they  were  derived, 
they  give  back  the  precise  amount  of  force  that  was  ex- 
pended in  separating  them.  This  coming  together  again, 
with  the  great  development  of  force  in  the  form,  of  light 
and  heat  which  accompanies  it,  constitutes  what  we  call 
combustion,  and  the  amount  of  the  force  thus  restored  is 
found  equal  in  heat  to  the  17,000  units  which  constituted 
the  heat  of  dissociation.  The  two  substances  now  form 
the  vapor  of  water.  And  this  vapor,  in  being  condensed 
into  liquid  water,  gives  back  again  the  heat  which  was  ex- 
pended in  originally  evaporating  it  —  that  is,  the  heat  of 
vaporization,  viz.,  9G2  units  per  pound;  or,  in  other  words, 
that  amount  of  heat  must  be  abstracted  from  it ;  or,  in  oth- 
er words  still,  it  must  be  cooled  to  that  extent  to  produce 
condensation.  It  is  now  liquid  water.  If  the  cooling  goes 
on  until  it  reaches  32°  Fahrenheit,  when  it  is  ready  to  be- 
gin to  freeze,  it  will  give  back  in  the  act  of  freezing — with- 
out growing  any  colder  to  the  hand  or  to  the  thermometer 
while  the  freezing  is  going  on — the  heat  of  liquefaction, 
namely,  142  units.  By  saying  that  it  will  give  out  that 
quantity  of  heat,  it  is  meant,  of  course,  that  that  amount 
must  be  abstracted  from  it — that  is,  it  must  be  cooled  to 
that  extent  in  order  to  freeze.  Thus  each  step  in  what 
may  be  called  the  ascending  process,  first  to  liquefaction, 
secondly  to  vaporization,  and  thirdly  to  decomposition  or 
dissociation,  requires  the  expenditure  of  a  certain  precise 
amount  offeree,  which,  measured  in  heat,  is  142  units  per 
pound  for  the  first  step,  962  for  the  second,  and  about 
17,000  for  the  third;  and  on  reversing  the  process,  that  is, 
in  returning  in  a  downward  direction,  as  it  were,  precisely 
these  amounts,  either  in  heat  or  its  equivalent  in  some  oth- 
er form  of  force,  will  be  given  out,  or  must  be  abstracted, 
at  each  of  the  three  grand  steps  of  the  descent. 
F 


122  HEAT. 

The  reader  who  has  given  careful  attention  to  the  prin- 
ciples explained  in  this  chapter  will  now  be  prepared  to 
consider,  in  the  next  three  chapters,  the  nature  of  the  solar 
energy — which  is  the  fountain  from  which  nearly,  if  not  all 
the  movement  and  action  which  are  witnessed  on  the  earth 
comes — and  to  follow  this  energy  in  the  three  principal 
circuits  which  it  takes  in  producing  the  wonderful  phenomv 
ena  which  we  witness  on  the  srlobe. 


FORCE    OF    WIND.  123 


CHAPTER  IX. 

THE    FOUR    CIRCUITS    OF   SOLAR    ENERGY. 
1.  THROUGH  THE  MEDIUM  OF  THE  AIR. 

As  was  said  in  the  last  chapter,  the  source  of  nearly  all 
the  action  of  every  kind  which  we  see  taking  place  around 
us  on  the  earth  is  the  radiation  from  the  sun.  It  requires 
a  careful  tracing  of  the  connection  of  causes  and  effects  to 
convince  us  to  how  great  an  extent  this  is  true;  and  there 
are  many  examples,  both  of  gentle  and  of  energetic  action, 
taking  place  on  the  earth's  surface,  which  it  would  seem  at 
first  was  impossible  to  refer  in  any  way  to  the  agency  of 
the  solar  rays. 

The  scene  represented  in  the  following  engraving,  for  ex- 
ample, shows  the  operation  of  forces,  in  the  one  case  ut- 
terly uncontrollable  by  human  power,  and  consisting  in  the 
onset  of  waves  upon  the  rocky  coast  with  an  energy  suffi- 
cient to  break  down  and  wear  away  the  hardest  rocks,  and 
in  the  other  made  entirely  subject  to  the  will  of  man,  and 
employed  by  him  in  gently  wafting  his  vessel  over  the 
stormiest  seas.  It  would  not  be  easy  for  an  uninstructed 
mind  to  see  how  the  action  of  such  forces  as  these  could  be 
traced  back  to  the  power  inherent  in  the  gentle  shining  of 
the  sun ;  but  we  shall  see  in  the  course  of  this  chapter  that 
this  is  really  true,  and  in  the  following  chapters  we  shall 
have  examples  of  still  more  extraordinary  transformations. 

The  solar  radiation  is  known  to  exist  in  three  forms,  and 
there  may  perhaps  be  others  that  are  not  known.  The 
three  forms  are  light,  heat,  and  a  third  class  of  rays  which, 
though  they  awaken  no  sensation  in  us,  are  capable  of  pro- 


124  THE    FOUK    CIRCUITS    OF    SOLAR    ENERGY. 


^ 


WOEK  OP  THE   BUN. 

ducing  remarkable  chemical  effects,  and  they  are  conse- 
quently called  chemical  rays.  They  are  also  sometimes 
called  actinic  rays,  and  the  kind  of  energy  which  they  ex- 
ercise is  called  actinism. 

When  Lawrence  explained  this  distinctly  to  John,  he  ad- 
vised him  to  repeat  the  words  actinic  rays  and  actinism 


FORMS   OP   SOLAK   RADIATION.  125 

ten  times — counting  them  upon  his  fingers — in  order  to 
make  the  words  familiar  to  him  and  impress  them  upon  his 
memory,  and  also  to  establish  in  his  mind  the  idea  of  a  real 
and  substantial  efficiency  in  what  they  denote,  although 
this  efficiency  is  not  directly  perceptible  to  our  senses. 

"Suppose,"  said  he, "that  you,  who  can  see,  were  in  a 
country  of  blind  men — " 

"The  people  could  not  live,"  said  John, "if  they  were  all 
blind  together." 

"No,"  rejoined  Lawrence, "I  don't  suppose  that  a  whole 
community  of  blind  men  could  really  exist  long;  so  we 
will  suppose  that  you  were  a  teacher  in  a  blind  asylum, 
and  that  you  were  to  take  your  class  of  scholars  out  into 
the  sun,  and  let  them  feel  his  rays  upon  their  cheeks  as 
they  turned  them  toward  it ;  they  would,  of  course,  be  con- 
vinced of  the  existence  of  one  of  the  forms  of  solar  radia- 
tion by  the  feeling  of  warmth  which  they  would  experi- 
ence, but  they  would  have  no  idea  of  the  light — or  of  the 
various  colors  which  the  rays  of  light  produce — from  any 
sensation  of  their  own.  You  would  have  to  furnish  proof 
for  them  of  the  existence  of  that  portion  of  the  sun's  radia- 
tion in  some  other  way." 

John  admitted  this,  and  then  Lawrence  explained  to  him 
that  it  is  somewhat  the  same  with  the  third  kind  of  radia- 
tion— actinism,  which  produces  no  direct  effect  upon  our 
senses  of  sight  or  feeling,  but  which  is  abundantly  proved 
to  exist  by  certain  other  eifects  resulting  from  it  that  are 
of  a  very  marked  and  striking  character. 

These  three  kinds  of  radiating  force,  though  they  are  in 
very  close  and  intimate  union  as  they  issue  from  the  sun, 
and  continue  thus  combined  during  the  whole  period  of 
their  journey  through  the  immense  space  which  they  have 
to  traverse  in  coming  from  the  sun  to  the  earth,  may  be 
separated  from  each  other  very  easily,  and  by  various  meth- 


126  THE    FOUR   CIRCUITS    OF    SOLAK    ENERGY. 

ods  when  they  arrive.  The  possibility  of  thus  separating 
light  and  heat,  for  example,  may  be  shown  by  a  very  sim- 
ple experiment,  namely,  by  interposing  a  pane  of  glass,  or 
any  portion  of  a  pane,  between  the  hand  or  the  face  and 
a  heated  stove  or  a  moderate  fire.  The  glass  will  not  in- 
tercept any  appreciable  portion  of  the  light,  for  the  fire  or 
the  form  of  the  stove  can  be  seen  through  it  perfectly  well, 
but  a  very  large  portion  of  the  heat  will  be  cut  off. 

There  are  various  other  methods  by  which  these  differ- 
ent forms  of  force,  as  they  issue  from  the  sun,  can  be  sep- 
arated, and  each  examined  and  experimented  upon  by  itself. 

The  solar  radiation,  then,  consisting  of  these  three  ele- 
ments combined,  traverses,  in  the  first  place,  the  vast  space 
which  separates  the  sun  from  the  earth — not  far  from  nine- 
ty millions  of  miles — in  a  mysterious  manner,  not  really 
well  understood ;  or,  at  least,  the  real  mode  of  its  transmis- 
sion has  not  been  positively  ascertained,  though  it  is  at  the 
present  time  the  prevailing  idea  among  scientific  men  that 
all  such  radiation  consists  in  the  communication  of  a  vibra- 
tory motion  through  a  peculiarly  subtle  medium  supposed 
to  fill  the  intervening  space,  and  which  has  been  named 
ether.  We  have  no  experience,  and,  of  course,  can  have  no 
conception  of  any  mode  of  communicating  force  except  as 
transmitted  motion,  and  to  render  such  a  transmission  of 
motion  possible  through  the  interplanetary  spaces,  we  have 
to  suppose  the  existence  of  an  intervening  ether,  extremely 
subtle,  but  capable,  through  a  certain  vibratory  or  undula- 
tory  action  among  its  particles,  of  being  the  means  of  the 
transmission  of  force. 

However  this  may  be,  the  solar  force,  in  its  compound 
form,  makes  its  way  by  some  means  through  the  interven- 
ing space,  and  on  its  arrival  at  the  surface  of  the  earth  it 
expends  itself  and  is  absorbed  chiefly  in  acting  upon  four 
classes  of  substances  which  it  here  encounters,  acting  in  a 


ACTION   OF  THE   SUN   UPON  THE    ATMOSPHERE.         127 

special  and  peculiar  manner  upon  each.    These  four  classes 
are — 

1.  The  Atmosphere. 

2.  Water  in  its  Liquid  and  Gaseous  States. 

3.  Water  in  the  form  of  Ice. 

4.  The  Organs  of  Animal  and  Vegetable  Life. 

The  present  chapter  will  be  devoted  to  the  consideration 
of  the  action  of  the  sun  upon  the  first  of  these  classes — that 
is,  in  following  out  the  course  of  that  portion  of  the  solar 
force  which  makes  its  grand  circuit  through  the  atmos- 
phere. 

The  force  has  to  pass  through  about  ninety  millions  of 
miles  of  space  without,  so  far  as  we  know,  meeting  with 
any  thing  to  interrupt  its  passage,  or  to  intercept  it  in  any 
way  except  as  regards  those  small  portions  of  it  which  fall 
upon  the  planets  and  their  satellites,  and  upon  our  moon ; 
and  as  these  bodies  are  seldom  directly  between  the  sun 
and  the  earth,  it  is  very  rarely  that  any  portion  of  the  radi- 
ation is  intercepted  which  the  earth  would  otherwise  re- 
ceive. 

It  is,  however,  only  an  extremely  minute  portion  of  the 
whole  amount  which  is  received  by  the  earth ;  for,  as  the 
solar  force  is  radiated  in  every  direction  from  the  sun,  and 
as,  consequently,  the  rays  diverge  from  each  other  as  they 
recede,  the  proportion  of  the  whole  which  falls  upon  the 
earth,  or  even  enters  its  atmosphere,  is  exceedingly  small. 

It  has  not  been  ascertained  with  precision  how  far  above 
the  surface  of  the  earth  the  atmosphere  extends.  The 
quantity  of  the  atmosphere  is  known  quite  accurately,  the 
whole  amount  having  been  ascertained  to  be  such  that  if 
the  density  were  uniform,  and  the  same  as  at  the  surface 
of  the  earth,  it  would  form  an  aerial  sea  enveloping  the 
earth  to  a  depth  of  about  five  miles  and  a  half.  But  the 
density  is  by  no  means  uniform ;  for  the  substance,  being 


128  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

exceedingly  elastic,  the  upper  portions  are  greatly  expand- 
ed, the  lower  portions  being  enormously  condensed  by  the 
weight  of  all  that  is  above  them.  Or,  to  express  the  same 
idea  in  other  words,  the  air  becomes  greatly  expanded  as 
we  ascend  from  the  surface,  the  successive  portions  swell- 
ing into  a  more  and  more  rarefied  condition  as  the  weight 
of  the  quantity  pressing  upon  them  from  above  diminishes. 

The  most  accurate  observations  and  calculations  which 
have  been  made  seem  to  indicate  about  forty-five  miles  as 
the  height  above  which  the  air  either  ceases  to  exist,  or 
becomes  so  extremely  attenuated  as  to  produce  no  percep- 
tible effect  upon  the  radiation  entering  it. 

This  height  is  much  less,  in  proportion  to  the  magnitude 
of  the  earth,  than  most  people  would  be  inclined  to  imag- 
ine. On  a  globe  of  sixteen  inches  in  diameter  the  whole 
forty-five  miles  would  be  represented  by  a  covering  not 
thicker  than  one  of  the  covers  of  this  book. 

But,  however  thin  this  covering  may  be  in  comparison 
with  the  size  of  the  earth,  the  space  through  which  the 
solar  radiation  has  to  pass  is  very  considerable  in  reference 
to  any  of  our  ordinary  terrestrial  standards.  When  we  re- 
flect that  the  loftiest  mountains  rise  to  a  height  of  only 
five  or  six  miles,  we  must  admit  that  forty-five  miles  is  a 
very  considerable  altitude ;  and  as  soon  as  the  rays  enter 
the  atmosphere  at  this  height,  they  begin  at  once  to  part 
with  some  portion  of  their  force.  So  far  as  we  know,  it  is 
force  of  the  heat-producing  rays,  rather  than  the  light-pro- 
ducing, or  the  chemical  rays,  that  is  first  imparted. 

And  here  I  must  explain  some  terms  which  arc  used  in 
scientific  books  to  express  the  phenomena  connected  with 
the  movements  of  heat  and  light,  and  which  it  is  important 
that  the  reader  should  understand.  That  portion  of  the 
heat  or  light  which  passes  through  any  medium,  such  as 
air,  water,  or  glass,  is  said  to  be  transmitted. 


OPACITY    AND   ATHERMANCY.  129 

That  portion,  on  the  other  hand,  which  is  turned  back 
from  its  course,  is  said  to  be  reflected. 

That  portion  which,  without  being  turned  back,  is  bent 
somewhat  out  of  its  direct  course,  but  still  goes  on,  is  said 
to  be  refracted. 

And,  finally,  that  portion  which  is  intercepted  entirely, 
and  expends  itself  in  effecting  changes  in  the  condition  of 
the  medium  itself,  or  of  substances  that  it  contains,  is  said 
to  be  absorbed. 

And  now  for  two  other  important  definitions. 

Any  medium  that  allows  light  to  pass  freely  through  it 
or  from  it,  without  absorbing  any  portion  of  it,  is  said  to 
be  transparent. 

If  it  does  not  allow  the  light  to  pass,  it  is  said  to  be 
opaque. 

And,  on  the  other  hand,  any  substance  which  allows  heat 
to  pass  freely  through  it  without  being  absorbed,  that  is 
to  say,  without  detaining  any  portion  of  it  to  effect  changes 
in  its  own  condition,  is  said  to  be  diathermant. 

If  it  does  not  allow  heat  to  pass  through  it,  it  is  said  to 
be  opaque  to  heat. 

When  Lawrence  explained  the  meaning  of  the  word  di- 
athermant to  John  and  Rick,  as  he  did  at  one  time  when 
they  were  in  the  shop  with  him  together,  he  advised  them 
both  to  repeat  the  word  ten  times,  counting  upon  their 
fingers.  This  was  his  usual  custom  when  he  taught  young 
persons  any  new  scientific  names,  in  order  to  fix  them  in 
their  memories,  and  I  think  it  is  an  excellent  practice  to 
be  adopted  by  persons  of  any  age  when  they  meet  with 
any  new  scientific  term. 

John,  when  Lawrence  asked  him  to  repeat  the  word  di- 
athermant in  this  way,  did  not  stop  when  he  repeated  it 
ten  times,  but  went  on  to  twenty.  As  for  Rick,  he  did  not 
repeat  it  all.  He  said  he  did  not  care  much  about  the  word. 
F2 


130  THE   FOUR    CIRCUITS    OF   SOLAR   ENERGY. 

Some  persons  might  at  first  imagine  that  all  those  me- 
dia* which  allow  of  a  free  passage  of  light  through  them 
would  also  allow  the  free  passage  of  heat,  so  that  the  word 
transparency  would  answer  for  both  properties.  But  this 
is  by  no  means  the  case,  as  we  have  seen  in  the  effect  pro- 
duced by  the  pane  of  glass,  which  allows  the  light  radi- 
ated from  the  stove  to  pass  through  it  very  freely,  while  it 
intercepts  the  heat.  Glass  will  allow  heat  that  is  of  a  very 
high  intensity — such  as  that  from  the  sun — to  pass  through 
it  very  freely,  while  it  intercepts  and  absorbs  the  low  de- 
grees. 

Experiments  have  been  carefully  made  upon  a  great  va- 
riety of  substances,  and  it  is  found  that  the  same  substances 
possess  the  properties  of  transparency  and  diathermancy  in 
very  different  degrees.  Some  bodies  are  both  transparent 
and  diathermant.  One  of  the  most  diathermant  bodies 
known  is  rock  salt,  a  sheet  of  it  an  inch  thick  intercepting 
scarcely  a  perceptible  portion  of  the  heat  that  traverses  it; 
whereas  alum,  whether  in  the  solid  form  or  as  a  solution 
in  water,  though  equally  transparent  with  rock  salt — that 
is,  allowing  almost  the  whole  of  the  light  which  traverses 
it  to  pass  freely  through,  intercepts  almost  the  whole  of 
the  heat. 

Now  the  atmosphere  which  surrounds  the  earth  is  both 
transparent  and  diathermant  in  a  great  degree — that  is,  it 
allows  a  very  large  portion  of  both  the  heat  and  light 
which  enters  it  from  the  sun  to  pass  freely  through  it.  It, 
however,  intercepts,  or  absorbs,  as  the  phrase  is,  a  consider- 
able portion  of  both. 

The  moment,  therefore,  that  the  solar  radiation  enters 
the  air,  a  portion  of  the  heat  is  intercepted  and  absorbed, 
and  additional  portions  continue  to  be  absorbed  as  the  rays 
pass  on  downward  through  the  increasingly  denser  por- 

*  The  plural  of  medium  is  media,  ns  that  of  phenomenon  is  phenomena. 


RAREFYING    EFFECT.  131 

tions  of  it  toward  the  ground.  The  three  different  kinds 
of  rays — that  is,  those  of  heat,  of  light,  and  of  actinism — 
are  all  more  or  less  absorbed  in  this  transmission,  but  the 
chief  effects  appreciable  by  man,  that  are  produced  in  the 
action  of  the  sun  upon  the  air,  are  due  to  the  absorption 
of  the  heat  rays. 

The  force,  then,  of  heat,  whatever  may  be  the  actual  form 
or  nature  of  it  as  it  issues  from  the  sun — that  is,  whether  it 
consists  in  a  vibratory  motion  in  the  substance  of  a  subtle 
ether  filling  all  space,  or  in  some  other  condition  incom- 
prehensible to  us — on  entering  the  earth's  atmosphere,  ex- 
pends itself  in  separating  forcibly  the  particles  of  air  from 
each  other — that  is,  in  expanding  the  air,  and  so  rarefying 
it  and  making  it  lighter,  and  thus  enabling  the  colder  air 
around  to  buoy  it  up  by  falling  by  its  side,  or  by  flowing 
underneath  it  in  currents  slightly  descending.  Thus  the 
force  from  the  sun,  by  making  lighter  one  portion  of  the 
air,  calls  into  action  the  falling  force  of  other  portions  which 
have  been  previously  made  lighter  and  lifted  in  the  same 
way. 

This  effect,  which  is  comparatively  slight  in  the  upper 
regions  of  the  atmosphere,  where  the  air  is  very  rare  and 
extremely  pure, becomes  much  greater  as  the  rays  approach 
the  earth.  Here  the  air  itself  becomes  more  dense,  and,  of 
course,  absorbs  more  of  the  heat.  Then,  in  addition  to  this 
increasing  density,  the  air  near  the  surface  contains  a  vast 
amount  of  foreign  substances,  consisting  of  particles  of 
dust  raised  by  the  wind — of  smoke  produced  by  combus- 
tion, and  composed,  in  a  great  measure,  of  atoms  of  carbon 
too  minute  to  be  individually  seen,  but  forming  together  a 
haze  which  has  great  power  to  intercept  and  absorb  the 
heat — and  vapors  of  water,  which,  even  when  they  are  so 
perfectly  pervious  to  light — in  other  words,  so  transparent 
that  they  can  not  be  seen  at  all,  have  still  a  great  power 


132  THE   FOUR   CIKCUITS   OF   SOLAK   ENEEGY. 

to  intercept  and  absorb  the  heat.  Then,  besides  the  effect 
of  these  foreign  substances  in  the  air  in  those  portions  of 
it  which  lie  near  the  surface  of  the  ground,  a  large  portion 
of  the  rays  which  make  their  way  through  these  obstruc- 
tions fall,  when  they  reach  the  ground,  upon  sandy  deserts 
or  arid  rocks,  and  are  reflected  from  them  back  into  the  air 
again,  while  even  those  that  are  actually  received  into  the 
ground,  and  expend  themselves  in  warming  it,  are,  to  a 
great  extent,  radiated  again  into  the  air  when  the  ground 
has  become  heated  by  them  to  a  certain  degree. 

Thus,  from  all  these  causes  combined,  a  very  large  por- 
tion of  the  force  which  comes  to  the  earth  from  the  sun  in 
the  form  of  heat  is  expended  in  warming,  and,  consequent- 
ly, in  expanding  or  rarefying  the  air,  and  producing  mo- 
tions in  it,  thus  affording  one  of  the  grandest  examples  in 
nature  of  the  conversion  of  heat  into  mechanical  force. 

We  might  well  imagine,  at  first  thought,  that  so  quiet 
and  gentle  an  influence  as  the  shining  of  the  sun  could 
only  result  in  producing  currents  of  very  moderate  veloc- 
ity, which  could  never  lead  to  the  violent  commotions  and 
terrible  effects  which  we  see  sometimes  produced  by  the 
wind.  But  the  force  that  is  brought  into  action,  though 
not  perceptibly  very  great  in  any  circumscribed  portion 
of  it,  becomes  vast  in  its  accumulations.  For  example, 
when,  during  the  whole  of  a  long  summer's  day,  the  rays 
of  the  sun  pour  down  upon  the  Desert  of  Sahara — a  large 
portion  of  them  being  intercepted  on  the  way,  and  of  those 
that  reach  the  rocks  and  the  sand  a  large  portion  being  re- 
flected again  into  the  air — the  total  effect  produced  over 
so  large  an  area  is  enormous.  The  air,  rarefied  and  light- 
ened, is  buoyed  up  and  made  to  flow  over  the  colder  air 
above ;  and  when  we  consider  that  the  weight  of  the  air 
over  every  square  inch  of  surface  is,  upon  an  average,  not 
less  than  fifteen  pounds,  we  shall  see  that  the  momentum 


HCKEICANE 


INCESSANT  MOVEMENTS.  135 

of  the  mass  which  will  tend  to  flow  in  below  from  the  sur- 
rounding oceans  and  continents  must  be  very  great.  The 
motion  of  the  inflowing  air  in  such  cases  is  complicated  by 
effects  produced  by  the  rotary  motion  of  the  earth,  of  which 
the  air,  of  course,  in  the  different  zones,  partakes,  and  is  de- 
flected by  the  action  of  it  as  it  passes  from  one  zone  to  an- 
other. At  the  same  time  there  are  other  deserts,  and  other 
regions  of  arid  rocks,  and  vast  tracts  of  fields  and  forests^ 
and  great  expanses  covered  with  ice  and  snow,  each  pro- 
ducing its  own  characteristic  effect  in  the  rarefaction  or 
condensation  of  the  air. 

The  consequence  is,  that  the  atmosphere  surrounding  the 
earth,  through  the  effects  resulting  from  its  power  of  ab- 
sorbing the  heat  of  the  sun,  is  kept  in  an  almost  continual 
turmoil.  Currents  and  counter  currents  are  set  in  motion 
above  and  below,  over  every  continent  and  every  sea,  as 
the  air  is  affected  by  the  constantly  changing  aspect  of  the 
surface  of  the  land,  and  of  the  position  of  the  sun,  and  the 
condition  of  the  clouds  in  the  sky.  In  many  cases  the  in- 
fluences of  all  these  various  forces  become  combined  and 
concentrated,  and  the  action  is  thus  enormously  intensified, 
producing  whirlwinds  and  tornadoes  by  which  houses  are 
demolished,  and  trees  broken  through  their  stems  or  torn 
up  by  the  roots. 

In  other  cases  the  contending  forces  happen  to  be  so 
nearly  in  equilibrium  that  for  a  time,  and  sometimes  over 
a  considerable  region  of  land  or  sea,  the  air  is  almost  en- 
tirely at  rest ;  and  it  may  be,  moreover,  in  such  cases,  so 
tempered  in  respect  to  its  heat,  in  relation  to  the  warmth 
of  our  bodies,  that  we  walk  in  it  amid  green  fields  or  gar- 
dens blooming  with  flowers,  or  along  the  shore  of  the  sea, 
and  feel  nothing  but  the  gentlest  and  balmiest  zephyrs  fan- 
ning our  cheeks — zephyrs  so  gentle  that  they  scarcely  causo 
the  most  delicately  poised  aspen  to  quiver  on  its  stem. 


136  THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

Even  in  winter  this  equilibrium  of  the  vast  forces  acting 
upon  the  air  is  not  unfrequently,  for  some  hours,  so  com- 
plete that  the  smokes  from  the  chimneys  ascend  toward 
the  sky  without  the  slightest  apparent  deflection  on  any 
side. 

There  is  something  very  remarkable  about  the  different 
velocities  of  the  wind  in  different  places  and  at  different 
times.  The  instrument  by  which  the  rate  of  its  movement 
is  measured  and  registered  is  called  an  anemometer.  One 
of  the  most  usual  forms  is  shown  in  the  engraving. 


It  is  formed  of  four  hemispherical  cups  placed  upon  the 


THE    ANEMOMETER.  137 

arms  of  a  horizontal  cross  in  such  a  manner,  as  shown  in 
the  engraving,  that  they  cause  the  cross  to  revolve  with  a 
rapidity  in  some  degree  proportioned  to  the  velocity  of  the 
wind  impelling  them.  The  velocity  of  the  rotation  is  usu- 
ally about  one  third  that  of  the  wind. 

The  cross  carries  with  it  a  vertical  axis  which  is  connect- 
ed with  clock-like  mechanism  below,  by  means  of  which 
the  result  of  any  observation  may  be  determined  numer- 
ically. 

For  the  cross,  in  being  carried  round  by  the  wind,  carries 
the  clock-work  below,  which,  by  means  of  the  endless  screw 
seen  under  the  lower  edge  of  the  dial-plate,  is  made  to  re- 
volve in  correspondence  with  it,  though  much  more  slowly 
in  degree.  In  order,  then,  to  ascertain  the  velocity  of  the 
wind  at  any  time,  the  observer  has  only  to  observe  how 
large  a  space  on  the  graduated  arc  the  index  passes  over 
in  a  given  time — five  minutes,  for  example.  This,  when 
properly  corrected  for  the  effect  of  the  mechanism  in  di- 
minishing the  rate  of  motion,  and  for  the  loss  of  two  thirds 
of  the  amount  in  the  revolution  of  the  cross,  will  give  ap- 
proximately the  velocity  of  the  W7ind  that  has  passed  the 
place  of  observation  during  the  period  observed. 

This  particular  instrument,  however,  is  only  one  of  a 
great  number  of  different  contrivances  that  have  been  de- 
vised for  ascertaining  the  velocity  of  the  wind.  This  ve- 
locity is  found  to  vary  from  the  least  perceptible  motion — 
that  of  a  mere  "breath  of  wind" — to  the  most  violent  hur- 
ricanes, in  which  the  air  has  a  movement  of  sixty,  eighty, 
and,  as  has  been  recently  observed  on  the  top  of  Mount 
Washington  in  winter,  more  than  a  hundred  miles  an  hour. 

Thus  what  would  be  called  a  gentle,  pleasant  breeze 
would  perhaps  have  a  velocity  of  five  or  six  miles  an  hour. 
A  stiff  breeze,  or  rising  gale,  such  as  would  make  it  neces- 
sary for  most  ships  at  sea  to  begin  to  take  in  sail,  would 


138  THE   FOUR   CIRCUITS   OF   SOLAK   ENERGY. 

be  perhaps  eighteen  or  twenty  miles  an  hour,  and  a  veloc- 
ity of  from  sixty  to  eighty  miles  an  hour  would  form  a  hur- 
ricane. It  would  be  well  for  young  men  reading  this  book 
to  fix  these  numbers  in  their  mind,  so  that,  when  witness- 
ing in  their  walks  winds  of  different  degrees  of  violence, 
they  may  have  some  approximate  idea  of  the  velocity  with 
which  the  air  is  moving. 

There  is  another  important  point  in  connection  with  the 
velocity  of  the  force  of  the  wind  on  which  it  is  important 
that  every  well-informed  person  should  have  some  tolera- 
bly definite  ideas,  and  that  is  the  amount  of  presstire  ex- 
erted by  it  upon  the  surfaces  of  such  substances  as  come 
in  its  way,  as  the  sides  of  buildings,  the  stems  and  branches 
of  trees,  the  sails  of  windmills  and  ships.  It  is  often  very 
necessary  for  engineers  to  know  this,  in  order  to  determine 
the  degree  of  strength  necessary  to  be  given  to  structures 
which  are  to  be  exposed  to  the  wind,  so  as  to  enable  them 
to  resist  its  force.  Very  careful  measurements  and  calcu- 
lations have  been  made  to  determine  the  degree  of  pressure 
exerted  for  each  different  rate  of  velocity,  and  the  results 
are  recorded  in  detail  in  extended  tables  for  the  use  of  sci- 
entific men.  It  is  only,  however,  a  few  of  the  results — to 
serve  as  specimens — which  are  important  for  the  general 
reader,  such,  for  example,  as  the  following,  where  the  sec- 
ond column  represents  the  pressure  on  each  square  foot  of 
the  resisting  surface.  This  means,  in  the  case  of  a  very 
stiff  breeze,  for  instance,  which  gives  a  pressure  of  one 
pound  per  square  foot,  that  the  effect  of  the  wind  upon 
one  side  of  a  board  one  foot  square,  exposed  to  its  action, 
would  be  the  same  as  that  which  would  be  produced  by  a 
weight  of  one  pound  suspended  by  a  cord,  which,  after 
passing  over  a  pulley,  was  attached  to  the  centre  of  the 
other  side  of  the  board. 

That  is  to  say,  that  the  deflection  of  such  a  board,  as  at 


FORCE    OF   THE   WIND. 


141 


5?ia-   X".-:"-"-"-x-; 

STIM  BEEEUT.       "-"-"£ 


VIIKHHUUK   OF  Till' 


A,  in  the  engraving,  if  supported  upon 
an  elastic  rod,  would  be  the  same  as  that 
atB. 

TABLE. 

Wind.  Pressure. 

Pleasant  Breeze i  Ib.  per  foot. 

Stiff  Breeze 1     "         " 

Gale 2.   " 

Hurricane L'O      "          " 


To  obtain  a  clear  idea  of  the 
force  represented  by  the  last  num- 
ber in  the  table,  you  must  imagine 
yourself  holding  one  end  of  a  rope, 
which  passes  over  a  pulley,  and  has 
twenty  pounds  suspended  at  the  other  end,  and  then  con- 
ceive of  such  a  force  as  this  acting  upon  every  square  foot 
of  the  sides  of  buildings,  and  of  the  stems  of  trees,  and  of 
the  sails  of  ships.  We  can  thus  help  ourselves  to  obtain 
some  conception  of  the  magnitude  of  it,  and  we  shall  no 
longer  be  surprised  that  trees  are  bent  and  broken,  that 
buildings  are  blown  down,  and  that  ships  are  thrown  upon 
their  beam  ends  and  capsized,  or  are  driven  irresistibly 
upon  rocks  and  breakers,  as  shown  in  the  engraving,  which 
represents  a  scene  at  Ha tt eras  Inlet  during  the  war. 

Of  course,  so  far  as  the  solar  force  is  transmitted  to  the 
trees,  and  to  buildings,  and  to  the  sails  of  ships,  and  takes 
eifect  upon  them,  it  is  lost  from  the  air.  And  there  is 
another  mode  by  which  the  force  is  transmitted  besides 
by  this  direct  impingement,  and  that  is  by  friction.  One 
would  not  at  first  suppose  that  the  friction  of  two  such 
fluids  as  air  and  water  upon  each  other  would  produce  any 
perceptible  effect •;  biit  a  current  of  air,  when  driven  over 
the  surface  of  water,  instead  of  flowing  smoothly  and  with- 
out disturbance,  communicates  to  it  enormous  quantities 


142  THE    FOUR    CIRCUITS    OF   SOLAR   ENERGY. 

of  its  force.  The  commencement  of  the  effect  is  a  rippling 
of  the  surface,  the  little  ripples  thus  produced  growing 
larger  and  larger  as  the  force  of  the  wind  continues  to  act 
upon  them,  until  billows  of  irresistible  power  are  formed, 
capable  of  moving  the  heaviest  rocks,  and  gradually  wear- 
ing away  and  destroying — as  is  shown  in  the  engraving 
near  the  commencement  of  this  chapter — the  most  compact 
and  solid  ledges  which  they  encounter  on  the  shore. 

The  currents  of  air  set  in  motion  by  the  sun  in  certain 
cases  of  their  interaction  upon  each  other  produce  a  rotary 
or  whirling  motion,  such  as  we  often  see,  on  a  small  scale, 
sweeping  along  the  street,  and  carrying  a  revolving  cur- 
rent of  dust  and  leaves  into  the  air.  These  phenomena 
take  place  sometimes  on  a  very  great  scale,  forming  torna- 
does on  land,  exercising  sufficient  force  to  sweep  into  them 
and  bear  away  trees,  houses,  and  sometimes  even  men  and 
animals  that  they  meet  with  in  their  course.  When  such 
whirlwinds  are  formed  at  sea,  they  seize  and  bring  into 
their  vortex  the  waters  of  the  billows  below  and  the  deluge 
of  falling  rain  descending  from  the  clouds  above,  and  thus 
form  what  is  called  a  water-spout. 

It  is  thought  to  be  a  very  wonderful  phenomenon  that 
the  motion  of  two  or  more  currents  of  wind  can  result  in 
producing  so  decided  and  powerful  a  whirling  motion,  and 
many  nice  mathematical  calculations  have  been  made  to 
show  by  what  precise  modes  of  action  such  a  result  can  be 
attained.  The  same  tendency,  however,  is  seen  in  the  cur- 
rents of  water  in  any  rapidly  flowing  stream,  which  pro- 
duce not  only  boilings  and  surgings,  but  also  distinct  whirl- 
ings innumerable,  whatever  may  be  the  precise  action  of 
the  forces  upon  each  other  in  producing  this  result. 

And  it  is  wonderful  to  think,  when  we  look  upon  so  sur- 
prising a  phenomenon  as  a  Avater-spout,  that  a  force,  issu- 
ing, in  the  first  instance,  in  the  form  of  a  radiation  from 


WATEB-SPOUT6, 


143 


THE   WATER-SPOUT. 


the  sun,  can  pass,  after  its  entrance  into  the  air,  through 
such  changes  in  the  character  and  duration  of  its  action 
that  it  can  finally  result  in  whirling  aloft  in  so  marvelous 
a  manner  such  a  mass  of  water  from  the  rolling  and  foam- 
ing surges  of  the  sea. 

The  friction  of  the  moving  air  over  the  surface  of  the 
water  produces  some  other  wonderful  effects  besides  its  ac- 
tion in  the  formation  of  the  waves.  When  the  wind  con- 


144  TUB    FOUR    CIRCUITS    OF   SOLAR   ENERGY. 

tinues  a  long  time  in  one  direction,  it  moves  bodily  a  large 
mass  of  water  in  that  direction,  forming  accumulations 
which,  though  relatively  to  the  magnitude  of  the  earth  very 
small,  are  absolutely,  in  regard  to  the  quantity  of  water 
which  they  contain,  very  large ;  and  these  accumulations, 
in  flowing  away  again,  aid  in  forming  the  remarkable  cur- 
rents which  are  found  constantly  flowing  in  every  part  of 
the  sea.  When  such  a  wind  coincides  with  the  action  of 
the  tide,  the  accumulation  of  water  in  the  harbors  upon 
the  coast  is  sometimes  very  great,  so  as  to  form  inunda- 
tions that  often  do  great  damage. 

Thus  the  force  derived  from  the  radiation  of  the  sun, 
and  entering  the  atmosphere  as  heat,  is  thence  transformed 
into  mechanical  motion,  which,  after  passing  through  many 
changes,  produces  a  great  variety  of  wonderful  phenomena. 
It  takes  effect  first  in  forcing  apart  the  particles  of  air,  so 
far  as  the  force  is  absorbed  by  them,  and  so  rarefying  it 
and  making  it  lighter.  We  must  not  suppose,  however, 
that  in  doing  this  it  gives  to  air  any  actual  ascending 
power,  but  only  that  it  diminishes  its  descending  power,  so 
as  to  give  the  greater  descending  power  of  the  colder  all- 
around  it  an  advantage  over  it,  thus  enabling  this  colder 
air  to  buoy  the  warmer  air  up,  for  the  warmest  and  light- 
est air,  if  unobstructed  and  unsupported,  would  fall  to  the 
ground  as  rapidly  as  a  mass  of  lead. 

It  is  not  the  lightness  of  the  light  air  in  the  balloon 
which  carries  the  balloon  up,  but  the  heaviness  of  the  heav- 
ier air  around  it  that  buoys  it  up ;  and  so  the  heat  of  the 
sun,  by  warming  the  air  that  absorbs  this  heat,  only  ena- 
bles the  air  that  has  become  cooler  to  flow  beneath  it,  and 
so  lift  it  out  of  its  way.  Thus  the  heat  of  the  sun,  taking 
the  form  offeree,  and  forcing  apart  the  particles  of  air,  is 
the  means  indirectly  of  raising  it  to  a  position  from  which, 


FORCE   INTERCEPTED   BY   MAN.  145 

in  its  subsequent  fall,  after  being  cooled  again,  it  can  pro- 
duce all  the  phenomena  of  winds  and  storms. 

A  very  considerable  part  of  the  force  manifested  by  this 
inflowing  and  underflowing  of  the  heavier  currents  of  air 
is  arrested  and  employed  in  the  service  of  man.  Every 
boy  who  flies  his  kite  Intercepts  and  uses  a  portion  of  it. 
Holland  employs  an  enormous  amount  of  it  in  turning  the 
countless  windmills  by  means  of  which  the  country  is  kept 
dry,  and,  up  to  the  present  time,  nearly  the  whole  of  the 
commerce  of  the  world  has  been  carried  on  by  the  force  thus 
derived  from  the  action  of  the  sun.  Men  are  now,  however, 
beginning  to  make  use,  on  a  large  scale,  of  the  force  lying 
latent  in  coal,  instead  of  that  of  the  icind,  for  this  purpose, 
though  this,  as  we  shall  see  in  future  chapters,  is,  in  its  or- 
igin, none  the  less  than  the  Avind,  derived  from  the  radia- 
tion of  the  sun. 

In  all  the  cases  brought  to  view  in  this  chapter,  though 
in  some  of  the  phenomena  described  the  water  is  incident- 
ally concerned,  the  effects  are  primarily  due  to  the  action 
of  the  solar  force  upon  the  air.  In  the  next  chapter  we 
shall  have  to  consider  a  class  of  phenomena  resulting  from 
the  action  of  the  solar  influence  directly  upon  the  water 
itself. 

G 


146  THE    FOUK   CIRCUITS    OF   SOLAR   ENERGY. 


CHAPTER  X. 

THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 
2.  THROUGH   THE   MEDIUM   OF  WATER. 
IN  the  last  chapter  we  considered  the  effects  of  the  en- 
ergy brought  in  radiation  from  the  sun  in  its  action  upon 
the  air,  including  some  of  the  effects  produced  upon  bodies 
of  water  by  the  changes  thus  induced  in  the  condition  of 
the  air.     In  this  chapter  we  have  to  inquire  into  the  effects 
produced  in  and  through  the  element  water  by  the  direct 
action  of  the  solar  force  upon  its  substance. 

1.  The  Expansion  of  the  Substance  of  the  Water  in  Lakes 

and  Seas. 

This  first  effect  of  the  solar  radiation  upon  the  water  is 
precisely  the  same  in  its  nature  with  that  which  is  pro- 
duced upon  the  air — that  is,  it  warms  and  expands  the  por- 
tion which  receives  and  absorbs  it,  and  thus,  by  lightening 
it,  allows  the  colder  water  in  the  vicinity  to  flow  down  be- 
neath it,  and  cause  it  to  float  away  over  the  surface  of  the 
colder  stratum.  There  is,  however,  this  remarkable  differ- 
ence in  the  two  cases,  namely,  that  whereas  it  is  upon  the 
lower  portions  of  the  atmosphere  that  the  sun  acts  most 
powerfully,  it  is  upon  the  upper  portions — that  is,  upon  the 
surface  of  the  water,  that  they  produce  the  greatest  effect. 
The  sun  acts  upon  the  lower  portions  of  the  air  on  account 
of  the  greater  density  and  the  greater  opaqueness  to  heat 
of  these  lower  portions,  and  also  on  account  of  the  fact 
that  these  portions  lie  near  the  surface  of  the  earth  where 
the  rays,  after  once  passing  through,  are  reflected,  and  enter 


EFFECT    OF   HEAT    ON   CURRENTS    OF   WATER.  147 

it  again,  thus  exerting  a  double  action  upon  it.  In  the  case 
of  the  water,  on  the  other  hand,  the  chief  effect  is  produced 
upon  the  upper  portions,  for  the  rays  have  no  power  to  pen- 
etrate to  any  great  depth.  There  is,  of  course,  a  great  dif- 
ference in  the  effects  produced  by  applying  the  expanding 
force  at  the  bottom  and  at  the  top  of  any  fluid  mass,  since 
in  the  former  case  the  lightened  portions  have  the  whole 
mass  to  rise  through  by  the  buoyancy  that  is  imparted  to 
them,  while  in  the  latter  it  is  only  a  comparatively  gentle 
flow,  laterally,  over  the  surface,  that  is  produced  by  the  ex- 
pansion of  the  heated  part. 

And  then  the  air,  being  a  gas,  is  much  more  expansible, 
in  proportion  to  its  bulk,  by  the  absorption  of  a  given  quan- 
tity of  heat,  than  water  is.  Thus,  if  a  bladder  three  quar- 
ters filled  with  cold  air  were  to  be  laid  before  the  hot  fire, 
it  might  become  fully  distended  by  the  rarefaction  of  the 
gaseous  substance  within,  while,  with  such  a  quantity  of 
water  within  the  bladder,  the  distending  effect  produced 
by  the  expansion  that  would  result  from  the  same  amount 
of  heat,  though  real,  and  capable,  within  its  proper  limits, 
of  exerting  a  prodigious  force,  would  perhaps  be  scarcely 
perceptible  in  increasing  the  distention  of  the  bladder. 

Through  the  influence  of  both  these  reasons  combined,  it 
results  that  the  currents  produced  by  the  action  of  the 
solar  force  upon  the  air  are  vastly  more  powerful  than  those 
produced  in  the  water.  The  latter,  however,  though  com- 
paratively smaller,  are  absolutely,  and  in  reality,  enormous 
in  magnitude  and  extent.  The  effect  of  the  heat  of  the 
sun  and  of  warm  winds  in  heating  and  expanding  the  wa- 
ters of  the  sea  in  tropical  regions,  and  also  in  other  regions 
where  the  rays  of  the  sun  descend  upon  them  in  their  full 
force,  is  to  produce  currents  which  have  the  character 
and  effect  of  vast  rivers  in  the  sea,  some  of  them  being 
many  miles  wide  and  thousands  of  feet  in  depth,  and  flow- 


148  THE    FOUR   CIRCUITS    OF   SOLAR    ENERGY. 

ing  at  the  ordinary  speed  of  rivers  upon  land.  The  water 
of  the  whole  ocean  is  kept  in  what  might  be  called  a  per- 
petual turmoil  by  the.  flow  and  counterflow,  the  opposings, 
the  combinings,  and  the  collisions  of  the  currents  thus 
formed,  consisting  in  the  main,  or  rather  in  a  great  meas- 
ure, of  the  colder  water  from  the  poles  flowing  in  from  be- 
low, and  floating  and  bearing  away  the  warmer  water 
above.  There  are,  however,  many  currents,  of  enormous 
magnitude  and  extent,  which  are  different  in  their  opera- 
tion and  effect  from  these,  being  produced  by  the  action 
of  prevailing  winds.  The  force  and  direction  of  these  is, 
of  course,  determined  by  the  force  and  direction  of  the 
winds  which  cause  them.* 

2.  Vaporization  of  Water. 

The  effects  which  have  thus  far  been  considered,  both  in 
the  case  of  air  and  water,  are  due  to  the  expansion  of  bulk 
in  those  substances  by  the  solar  energy,  without  any  other 
change  in  their  condition.  But  there  is  another  effect  pro- 
duced in  the  case  of  water,  which  consists  in  a  change  of 
form  from  a  liquid  to  a  gaseous  state ;  the  air,  of  course, 
being  already  a  gas,  is  not  subject  to  any  change  in  this 
respect. 

It  has  already  been  explained  in  a  previous  chapter  that 
a  very  large  amount  of  heat  is  absorbed  and  rendered 
"  latent,"  as  the  phrase  is,  in  converting  water  from  the 
liquid  to  the  gaseous  form,  the  amount  being  about  962 
units  for  every  pound  of  water  so  changed ;  that  is  to  say, 
if  a  portion  of  cold  water — of  the  temperature,  for  example, 
which  it  has  when  just  melted  from  ice,  namely,  32° — is 
placed  in  a  boiler  over  a  fire,  then  for  each  unit  of  heat 
which  each  pound  of  it  receives  it  is  raised  in  temperature 

*  The  character  and  extent  of  these  various  ocean  currents  is  more  ful- 
ly explained  in  the  volume  of  this  series  entitled  WATEK  AND  LAND. 


HEAT   OP   VAPORIZATION,  149 

one  degree  till  it  acquires  the  temperature  of  212°.  This 
would  require,  of  course,  the  absorption  by  the  water  of 
180  units,  for  each  unit  raises  the  temperature  one  degree, 
and  180°  added  to  32°  makes  212°. 

After  this,  though  the  heat  continues  to  enter  as  fast  as 
ever  through  the  bottom  of  the  boiler,  the  water  is  not 
made  any  hotter  by  it,  the  whole  of  the  heat  so  entering 
being  employed  in  some  mysterious  Avay  in  converting  the 
liquid  water  into  a  vaporous  form ;  and,  what  is  very  won- 
derful, it  requires  962  units  for  every  pound  of  water  to 
effect  this  change — that  is  to  say,  over  five  times  as  much 
heat  is  expended  in  converting  water  at  the  boiling  point 
into  steam,  and  that  without  making  the  substance  of  it 
any  hotter,  as  would  serve  to  raise  the  same  water  from 
the  ice-cold  condition  to  the  boiling  point ! 

The  boiling  of  water  by  such  a  process  as  is  described 
above  is  the  most  familiar  example  we  have  of  the  conver- 
sion of  water  into  steam — that  is,  changing  it  from  the 
liquid  to  the  gaseous  form.  But  substantially  the  same 
change  is  effected  in  a  great  variety  of  other  modes.  When 
water  "dries  up"  after  being  spilled  upon  the  floor,  the 
•  change  that  takes  place  is  the  vaporization  of  the  water, 
chiefly  by  the  action  of  the  heat,  or,  at  any  rate,  through 
the  absorption  of  heat.  This  heat  may  be  imparted  to  it 
by  the  beams  of  the  sun,  or  by  the  warmth  of  the  fire  shin- 
ing upon  it,  or  else  by  the  heat  which  it  can  draw  from 
the  surrounding  objects.  This  is  the  reason  of  the  cooling 
effect  which  water  drying  off  from  a  floor,  or  a  pavement, 
or  from  the  skin  of  the  face  or  the  hand  produces.  The 
process  is  aided,  it  is  true,  by  an  attraction  between  the 
particles  of  the  surrounding  air  and  those  of  the  water  in 
these  cases,  the  water  being  dissolved,  as  it  were,  in  the  air 
somewhat  as  a  lump  of  sugar  is  dissolved  by  water  in  which 
it  is  immersed.  But  the  process  can  not  go  on  any  faster 


150  THE    POUR   CIRCUITS    OF   SOLAR   ENERGY. 

than  the  water  is  converted  into  vapor,  and  this  can  not 
be  effected  without  the  full  complement  of  heat  being  de- 
rived from  some  source  or  other,  namely,  about  962  units 
of  heat  for  every  pound  of  water  so  converted  into  vapor, 
though  varying  somewhat  in  different  cases  through  the 
influence  of  difference  of  pressure  and  some  other  condi- 
tions moderately  affecting  the  result. 

The  point,  then,  to  be  specially  borne  in  mind  is  that  a 
certain  definite  portion  of  the  force  comprised  in  the  solar 
radiation  is  employed  in  the  vaporization  of  water  upon 
the  earth's  surface — namely,  that  which  is  equivalent  to 
about  962  units  of  heat  for  every  pound  of  water  so  evap- 
orated; and  that  this  force,  combining  with  the  water  in 
the  form  of  heat,  is  not  lost  or  diminished  in  the  slightest 
degree,  but  remains  in  a  latent  form,  that  is,  entirely  con- 
cealed from  our  observation,  in  the  vapor,  and  that  it  re- 
mains there  without  any  increase  or  diminution  while  the 
water  continues  in  that  state ;  and,  finally,  when  the  vapor 
is  condensed  into  liquid  water  again,  it  will  deliver  up  pre- 
cisely this  amount  of  force,  perhaps  in  the  form  of  heat 
and  perhaps  in  some  other  form,  but  in  quantity  neither 
less  nor  more  than  that  which  was  originally  imparted  to 
it  by  the  sun. 

This  is  one  example  of  what  is  called  by  scientific  men 
the  conservation  of  energy,  which  expression  denotes  the 
actual  permanence  and  unchangeableness  in  amount  of  ev- 
ery portion  of  force,  using  the  term  in  the  sense  of  energy. 
The  force  may  change  its  form,  it  may  for  a  time  pass  en- 
tirely out  of  view,  its  action  may  be  suspended  for  a  time,  it 
may  be  accumulated  and  concentrated,  and  thus  increased 
in  tensity,  or  it  may  be  divided  and  dispersed,  but  no  in- 
crease or  diminution  can  by  any  possibility  be  made  in  its 
amount  by  the  passing  of  any  portion  of  it  out  of  exist- 
ence. 


QUANTITY  OP  HEAT  ABSORBED.  151 

So  far,  then,  as  the  radiation  from  the  sun  falls  upon  and 
enters  into  water  upon  the  earth,  whether  upon  that  which 
forms  the  surface  of  the  rivers  or  the  sea,  the  drops  of  dew 
upon  the  grass,  the  dampness  of  the  ground,  or  the  minute 
globules  of  liquid  water  floating  in  the  air  which  constitute 
the  substance  of  mists,  fogs,  and  clouds,  the  first  effect  is 
to  expand  it  in  its  liquid  form,  and  so  make  it  somewhat 
more  buoyant  than  it  was  before,  and  the  next  is  to  con- 
vert portions  of  it  into  vapor,  by  a  mysterious  process, 
which  has  the  effect  of  storing  in  it,  in  a  concealed  form, 
an  amount  offeree  equal  to  that  contained  in  962  units  of 
heat  for  every  pound  of  water  so  converted. 

There  is  another  important  thing  to  be  observed — a  fact 
which  will  perhaps  surprise  the  reader  if  he  has  never  had 
his  attention  called  to  it,  and  that  is,  that  the  vapor,  after 
it  is  formed,  is  precisely  as  heavy,  that  is,  that  it  weighs 
precisely  as  much  as  the  water  which  formed  it.  We  call 
it  light  because,  bulk  for  bulk,  it  is  lighter  than  the  all- 
around  it,  and  so  is  buoyed  up  and  made  to  ascend.  But 
a  pound  of  water  converted  into  steam  produces  a  pound 
of  steam,  which  weighs  absolutely  just  as  much  after  its 
conversion  as  before,  on  the  principle  that  a  pound  of  lead 
is  no  heavier  than  a  pound  of  feathers. 

The  vapor  of  the  water,  therefore,  produced  by  the  ac- 
tion of  the  sun,  rises  into  the  air,  carrying  with  it  the 
stores  of  force  which  it  has  absorbed  from  the  sun.  As  it 
ascends,  it  acquires  from  the  air  around  it,  which  buoys  it 
up,  a  falling  force  in  proportion  to  the  height  to  which  it 
is  raised,  which  falling  force  will  take  effect  and  come  into 
action  as  soon  as  the  vapor  is  condensed  into  liquid  water 
again,  and  when  thus  changed  will  bring  it  down  in  drops 
of  rain.  It  has  also  the  heat  of  vaporization — 962  units  for 
each  pound — which  must  be  abstracted  from  it  by  the  cool- 
ness of  the  surrounding  air  in  the  higher  regions  of  the  at- 


152  THE   FOUK   CIRCUITS   OF   SOLAK   ENEKGT. 

mosphere,  in  the  process  of  being  condensed,  so  as  to  be 
formed  into  liquid  water  again. 

These  vapors,  being  borne  aloft  by  the  buoyant  force  of 
the  heavier  air  around  them,  and  carrying  with  them,  as  it 
were  in  store,  these  two  forms  of  force,  become  involved  in 
the  maze  of  aerial  currents,  which,  as  we  have  already  seen, 
are  continually  sweeping  through  the  upper  air;  and  here, 
as  fast  as  they  come  in  contact  with  portions  of  the  atmos- 
phere cool  enough  to  abstract  the  heat  stored  in  the  sub- 
stance of -them — that  is,  962  units  of  each  pound,  return 
to  the  liquid  state ;  and  inasmuch  as  the  whole  mass,  as  it 
thus  changes  its  condition,  is  enormously  reduced  in  size, 
each  several  portion,  of  course,  shrinking,  as  it  were,  into 
itself,  leaves  wide  interstices  between  itself  and  its  neigh- 
bors. It  is  in  this  way  that  fogs,  mists,  and  the  incipient 
drops  of  rain  are  formed,  all  of  which  consist  of  extremely 
minute  drops  of  liquid  water  floating  in  the  air. 

The  precise  manner  in  which  minute  globules  form  and 
group  themselves  into  masses  in  the  upper  regions  of  the 
air  is  affected  by  a  great  many  other  causes,  among  which, 
undoubtedly,  electricity  plays  a  very  important  part,  in 
a  manner,  however,  which  is  yet  very  little  understood. 
Sometimes  a  mass  of  cloud — that  is,  a  mass  which  consists 
simply  of  an  aggregation  of  minute  globules  of  water — will 
be  formed  in  the  midst  of  a  clear  and  transparent  sky  with- 
out any  visible  cause,  and  then,  after  floating  along  a  little 
way,  will  melt  away  again  and  disappear.  At  other  times, 
particularly  in  a  warm  summer  afternoon,  the  condensa- 
tion thus  begun  goes  on  with  great  rapidity ;  the  mass  in- 
creases in  density  till  it  becomes  black  to  our  view  on  ac- 
count of  its  intercepting  all  the  light  from  the  sun,  which, 
when  the  mass  of  condensed  vapor  is  thin,  passes  through 
and  illuminates  it,  and  the  globules  increase  in  magnitude 
till  they  fall  in  a  deluge  of  drops  to  the  earth  below.  There 


CLOUD   FORMATIONS.  155 

is  usually  a  great  development  of  electric  force  in  these 
cases,  showing  itself  in  the  flashes  of  lightning  and  the 
peals  of  thunder  which  usually  accompany  such  a  shower. 

At  other  times,  perhaps,  the  rising  vapors  from  the  earth, 
after  ascending  to  a  certain  height,  and  meeting  with  no 
air  sufficiently  cold  to  abstract  from  them  the  store  of  heat 
by  means  of  which  the  sun  has  produced  them,  have  spread 
themselves  out  horizontally  over  a  wide  area,  and  then  a 
current  of  much  colder  air  from  some  cause  flows  over 
them  and  produces  a  moderate  condensation,  a  broad  and 
thin  sheet  of  haziness  is  formed,  covering  the  whole  sky. 

In  these  and  in  other  ways,  through  causes  that  are  not 
well  understood,  a  great  variety  of  cloud  formations  are 
produced  from  time  to  time  in  the  sky.  The  principal  va- 
rieties of  these  formations  have  received  definite  names. 
The  engravings  give  specimens  of  the  more  striking  forms, 
with  the  names  by  which  they  are  designated  as  adopted 
at  the  National  Signal  Office  in  Washington,  and  employed 
in  the  records  kept  at  the  various  stations  throughout  the 
United  States  that  are  under  its  charge. 

The  clouds,  especially  in  pleasant  weather  when  the  sky 
is  tolerably  clear,  tend  to  form  in  feathery  or  fleecy  masses, 
designated  in  the  engraving  of  primary  forms  by  one  bird. 
These  are  called  cirri,  the  singular  form  of  the  word  being 
cirrus.  The  second  of  the  primary  forms  is  the  cumulus, 
which  consists  of  large  rounded  masses  terminated  above 
by  dome-like  summits,  which,  being  illuminated  by  the  rays 
of  the  sun  shining  upon  the  upper  portions,  have  often  a 
brilliantly  white  appearance,  while  the  lower  portions  of 
the  mass  are  dark,  being  sunk  in  shadow.  Specimens  of 
the  cumuli  are  seen  in  the  centre  of  the  picture.  As  the 
condensation  goes  on,  the  globules  of  water  grow  larger, 
until  they  fall  in  copious  showers  of  rain  to  the  ground  be- 
low, as  shown  in  the  representation  which  is  seen  at  the 


156  THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

left  hand  of  the  picture,  and  is  marked  by  the  four  birds. 
The  cumulus,  when  advanced  to  this  stage,  is  called  a  nim- 
bus. 

The  formation  of  cumuli  and  nimbi  goes  on  most  fre- 
quently and  rapidly  in  this  climate  in  summer  afternoons 
in  the  hottest  weather.  There  is  something  very  mysteri- 
ous and  very  little  understood  in  the  causes  of  this  ex- 
tremely rapid  condensation  of  masses  of  vapor  in  the  skies 
at  such  a  time.  The  violent  electric  discharges  which  ac- 
company the  action  show  that  the  phenomenon  is  connect- 
ed in  some  way  very  intimately  with  the  development  of 
the  electrical  force,  but  whether  as  cause  or  effect  it  is  very 
difficult  to  determine. 

There  is  another  formation  of  a  totally  different  kind 
from  these,  which  consists  in  a  comparatively  thin,  continu- 
ous, and  uniform  layer,  extending  over  regions  many  miles 
in  extent — sometimes,  indeed,  over  whole  countries,  and 
even  over  entire  continents.  We  know  that  they  are  thin 
by  the  amount  of  light  which  passes  through  them,  for  the 
under  surface  is  never  nearly  black,  as  in  the  case  of  the 
cumulus;  and  that  they  are  of  nearly  equal  thickness 
throughout  from  the  uniformity  of  the  tint  produced  by 
the  light  that  passes  through  them.  These  horizontal  lay- 
ers of  condensed  vapor  may,  perhaps,  be  produced  by  a 
stratum  of  air  above  flowing  over  one  below  that  is  highly 
charged  with  moisture,  so  as  to  form  a  continuous  conden- 
sation of  moderate  thickness  along  the  whole  plane  of  junc- 
tion. 

However  this  may  be,  the  fact  that  such  uniform  and  ex- 
tended layers  of  cloud  are  often  formed  is  very  clear,  and 
when  they  are  of  moderate  extent,  so  that  the  whole  of  one 
of  them  can  be  seen  by  a  spectator  at  a  distance  from  them, 
and  nearly  in  the  same  plane — that  is,  when  the  spectator 
is  so  placed  that  the  flat  cloud  can  be  seen  by  him  edge- 


COMBINATIONS    OP   CLOUDS.  159 

wise,  as  it  were,  it  assumes  in  appearance  a  long,  slender, 
and  needle-like  shape,  pointed  at  the  ends,  as  shown  by  the 
specimens  in  the  lower  part  of  the  engraving  of  Primary 
Forms,  and  marked  by  the  figures  of  two  birds.  Such  a 
formation  is  called  a  stratus.* 

These  three  primary  forms  are  combined  with  each  other 
in  various  ways,  as  shown  in  the  engraving  of  Secondary 
Forms. 

As,  for  example,  in  the  lower  right-hand  part  of  the  pic- 
ture, the  cumulus  is  seen  blended  into  the  stratus  below, 
forming  the  cumulostratus,  and  in  the  upper  portions  the 
strati,  and  cirri,  and  cumuli  in  various  forms  are  combined, 
or,  rather,  clouds  are  seen  partaking  of  the  character  of 
two  or  more  of  these  formations,  constituting  what  is  called 
a  cirrostrati  and  cirrociimuli.  In  some  of  these  cases  the 
vapor  is  seen  forming  itself  in  regular  divisions,  alternating 
with  portions  of  transparent  air,  like  a  series  of  waves  or 
mottled  patches  grouped  together  with  great  regularity. 
Persons  accustomed  to  observe  the  clouds  often  remark 
this  peculiarity  in  the  formation  of  them,  and  wonder  at  its 
cause.  It  seems  plainly  to  indicate  some  kind  of  wave-like 
or  pulsating  action  in  the  forces  concerned,  but  the  precise 
character  and  operation  of  the  cause  is  by  no  means  well 
understood. 

Now  the  thing  to  be  specially  observed  in  respect  to  the 
formation  of  clouds,  and  of  drops  of  rain  or  flakes  of  snovr 

*  It  may  be  well  to  remind  the  young  student  that  there  are  two  words 
of  nearly  the  same  etymological  meaning,  and  both  derived  from  the  Latin 
— one,  stratum,  the  plural  of  which  is  strata,  and  the  other  stratus,  which 
in  the  plural  becomes  strati.  Both  the  words  originally  denoted  simply  a 
spread,  whence  they  are  used  in  our  language  to  denote  a  layer  of  any  kind. 
The  two  forms  of  the  word  have,  however,  curiously  enough,  been  separa- 
ted in  their  use  in  our  language,  stratum  and  strata  being  employed  to  de- 
note layers  of  earth  or  rock  on  the  surface  of  the  ground,  and  stratus  and 
strati  being  confined  to  those  of  condensed  vapor  in  the  sky. 


160  THE    FOUR   CIRCUITS   OF   SOLAR   ENERGY. 

in  the  atmosphere,  and  on  the  knowledge  of  which  the  right 
understanding  of  this  class  of  the  phenomena  of  nature  de- 
pend, is  that  this  condensation  of  the  vapors  is  the  mode 
by  which  they  deliver  up  and  transfer  to  the  air  at  large 
the  enormous  force  which  they  have  imbibed  from  the  sun 
in  the  process  of  vaporization.  We  have  seen  that  the 
amount  of  this  force  in  the  form  of  heat  is  962  units  to  the 
pound,  which  is  enough  to  heat  four  or  five  pounds  of  very 
cold  water  up  to  the  boiling  point.  In  other  words,  every 
pound  of  water  which  rises  from  the  river,  or  the  sea,  or 
the  ground  in  vapor,  in  consequence  of  the  heat  of  the  sun 
which  it  absorbs,  carries  enough  heat  with  it  into  the  air 
to  warm — that  is,  to  make  less  cold — a  very  large  quantity 
of  air,  and  this  heat  it  must  leave  somewhere  in  the  air  be- 
fore it  can  be  condensed  and  come  down ;  for  it  can  not  be 
condensed  without  being  cooled,  and  it  can  not  be  cooled 
without  having  its  heat  abstracted  from  it  by  the  surround- 
ing bodies. 

Thus  the  drying  up  of  water  from  the  ground  by  the  sun 
is  the  charging  of  that  water  with  a  large  portion  of  the 
solar  energy,  to  be  wafted  into  the  air  and  borne  by  the 
aerial  currents  all  over  the  globe,  the  water  to  be  returned 
again  to  the  ground  in  rain  after  leaving  behind  it  the  store 
of  heat  with  which  it  has  been  intrusted.  And  it  can  not 
come  back  till  it  has  delivered  its  load,  which  load,  being  in 
the  form  of  heat,  is,  of  course,  most  easily  delivered  Avhere 
the  atmosphere  around  it  is  cold,  and  the  result  is  that  it 
spends  its  force  in  warming  the  air,  in  the  sense,  that  is, 
of  diminishing  the  cold  of  it  in  those  regions  and  times  in 
which  the  air  is  coldest — in  the  wintry  climates  and  in 
wintry  seasons,  over  the  summits  of  mountain  chains  and 
in  tropical  regions,  at  great  height  from  the  ground. 

The  amount  of  solar  force  thus  expended  upon  the  sur- 
face of  lakes,  rivers,  and  seas,  and  upon  the  moisture  on  the 


VASTNESS   OF  THE   STORED   FOKCE.  161 

ground  in  vaporizing  water  and  preparing  it  to  be  lifted 
into  the  air  by  the  downward  tendency  of  the  heavier  air 
around  it,  is  enormous  beyond  all  human  conception.  When 
we  stand  upon  the  bank  of  a  placid  lake  on  a  warm  sum- 
mer's day,  and  observe  its  aspect  as  the  beams  of  the  sun 
are  lying  upon  it  apparently  in  so  quiet  and  peaceful  a 
manner,  the  whole  scene  suggests  to  our  minds  only  ideas 
of  inertness  or  repose.  We  are  little  aware  of  the  vast 
force  which  the  sun  is  expending  in  separating  the  particles 
of  the  water  from  each  other  and  causing  them  to  ascend 
into  the  air.  In  certain  lights  we  sometimes  have  a  glimpse 
of  the  shimmer  produced  by  the  ascending  currents  of  air, 
but  we  have  very  little  conception  of  what  this  scarcely 
perceptible  movement  denotes,  nor  of  the  potent  agency 
which  the  ascending  currents  of  vapor-charged  air  have  to 
fulfill  before  the  water  contained  in  them  is  condensed  and 
returned  to  the  earth  again. 

This  process  necessarily  goes  on  with  the  greatest  ener- 
gy in  the  waters  of  tropical  seas,  where  the  solar  radiation 
exercises  its  greatest  power.  The  evaporation  is  here  so 
great  that  it  would  soon  produce  a  vast  depression  in  the 
water  through  all  the  region  were  it  not  for  the  continued 
inflow  from  the  surrounding  seas.  Millions  upon  millions 
of  tuns  of  water  are  vaporized  and  raised  into  the  air  every 
day,  each  pound  bearing  its  charge  of  962  units  of  heat,  and 
each  unit  representing  and  being  equivalent  to  a  force  suf- 
ficient to  raise  one  pound  772  feet  into  the  air!  The  im- 
agination is  confounded  in  attempting  to  picture  to  itself 
the  enormity  of  such  a  force,  and  yet  nothing  can  be  more 
certain  than  the  reality  of  it.  That  such  a  force  is  thus 
transferred  from  the  rays  of  the  sun  to  the  water  of  the  sea, 
and  that  it  does  produce  the  effects  here  ascribed  to  it,  are 
facts  as  well  established  as  any  truths  whatever  coming 
within  the  domain  of  human  knowledge. 


162  THE    FOUR    CIRCUITS    OF   SOLAR   ENERGY. 

And  yet  a  company  of  travelers  on  their  voyage  to  the 
West  Indies,  when  seated  under  an  awning  on  the  deck  of 
the  steamer  in  a  calm,  are  wholly  unconscious  of  what  is 
going  on  upon  the  placid  and  motionless  surface  of  the 
water  around  them.  They  must  have  an  awning  over  their 
heads  to  protect  themselves  from  the  solar  force,  but  they 
have  no  idea  of  the  enormous  work  which  that  force  is  per- 
forming so  silently  all  around  them  on  the  sunny  sea. 

The  heat  which  is  absorbed  by  the  water  in  being  vap- 
orized must  be  taken  from  it  in  some  way,  as  has  already 
been  said,  before  the  vapor  can  be  condensed  again,  and  so 
be  allowed  to  come  down.  It  can  be  taken  from  it  in  the 
air  above  in  no  other  way,  so  far  as  we  know,  but  by  being 
imparted  to  some  other  portions  of  the  air,  thus  making 
them  warmer — that  is  to  say,  less  cold.  They  do  this  to  a 
great  extent  jn  the  upper  regions  of  the  air  above  the  seas 
where  the  vapors  are  formed,  and  the  abundant  rains  for 
which  the  tropics  are  noted  are  the  result.  Other  portions 
deliver  their  stores  of  heat  to  cold  air  which  gathers  around 
the  summits  of  the  mountains,  and  others  still  are  wafted 
to  the  northward  and  southward,  where  they  exert  a  vast 
influence  in  mitigating  the  intense  cold  of  the  frigid  zone. 
It  is  thus  through  the  medium  of  watery  vapors,  conveying 
stores  of  solar  force  from  the  more  heated  to  the  colder  re- 
gions of  the  earth,  that  the  great  extremes  of  temperature 
which  would  otherwise  be  experienced  in  different  regions 
and  climes  are  modified,  and  a  powerful  tendency  to  equal- 
ization is  the  result — a  compensating  tendency  without 
which  some  portions  of  the  earth  now  forming  comfortable 
homes  for  man  would  be  rendered  uninhabitable  by  the 
heat,  and  others  by  the  cold. 

The  cooling  effect  of  a  flowing  stream  upon  the  air  along 
its  banks,  or  of  a  shower  falling  upon  the  heated  ground, 
or  of  the  sprinkling  of  a  floor  or  of  a  walk,  or  of  dipping 


COOLING   EFFECT   OF   VAPORIZATION.  163 

the  finger  in  water  and  then  holding  it  in  the  air,  or  even 
of  a  drop  of  water  that  falls  by  accident  upon  the  face  or 
hand,  is  due  to  this  cause,  namely,  the  great  quantity  of 
heat  that  is  drawn  into  the  water  from  the  surrounding 
substances  in  the  process  of  evaporation,  which  in  all  these 
cases  at  once  begins  to  take  place.  Moistening  the  hand 
with  oil  does  not  produce  this  cooling  sensation,  for  the  oil 
does  not  evaporate,  and  so  does  not  draw  any  more  heat 
from  the  flesh  than  just  enough  to  warm  the  substance  of 
it  up  to  the  warmth  of  the  flesh ;  and  if  it  is  as  warm  as  the 
flesh  beforehand,  it  produces  no  sensation  of  coldness  at  all; 
but  if  a  drop  even  of  warm  water  falls  upon  the  hand,  the 
sensation  of  heat  which  is  felt  for  a  moment  very  quickly 
disappears,  and  is  succeeded  by  a  sensation  of  cold,  for  it 
almost  immediately  begins  to  abstract  heat  from  the  hand 
to  enable  itself  to  assume  the  vaporized  form,  and  so  rise 
into  the  air. 

This  principle  explains,  too,  the  powerful  effect  of  water 
in  extinguishing  fires,  the  effect  being  due  to  the  vast  quan- 
tity of  heat  abstracted  from  the  burning  materials  by  the 
water  in  being  converted  into  vapor  by  it.  If  the  water 
acted  only  by  its  coldness  as  water,  it  would  produce  no 
more  effect  upon  the  fire  than  so  much  cold  sand ;  but  as 
the  water  is  instantly  converted  into  vapor  the  moment 
that  it  touches  the  fire,  and  as  each  pound  of  it  abstracts 
for  this  purpose  962  units  of  heat,  the  fire  is  soon  cooled  by 
it  below  the  point  of  ignition,  or,  as  we  say,  is  extinguished. 

And  now  we  come  to  another  branch  of  the  subject  un- 
der discussion — that  is,  to  another  class  of  effects  produced 
by  the  circuit  of  solar  force  through  the  air,  which  is  the 
falling  force  of  the  water  when  it  is  at  last  relieved  of  its 
charge  of  heat,  and  is  condensed  again,  so  as  to  descend  in 
rain ;  for  these  two  things  must  be  kept  distinct  in  the 


164  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

mind.  The  heat  which  each  pound  of  water  receives  from 
the  solar  radiation,  and  which  is  expended  in  converting  it 
into  vapor,  is  one  thing ;  the  lifting  force  which  is  exerted 
upon  this  vapor  after  it  is  formed,  by  the  colder  air  around 
it,  is  another.  We  have  already  seen  what  becomes  of  the 
heat,  its  destination  being  to  impart  itself  to  the  currents 
of  colder  air  which  it  encounters  in  the  higher  regions  of 
the  atmosphere.  But  after  the  vapor  has  thus  been  relieved 
of  its  heat,  and  has  been  recondensed  into  minute  globules 
of  water,  forming  clouds,  all  the  lifting  force  which  was  ex- 
erted upon  it  in  raising  it  remains  ready  to  act  again  in 
the  fall  of  it,  precisely  as  the  force  expended  in  raising  the 
weight  of  a  pile-driver  remains  in  store  and  in  suspense,  so 
to  speak,  in  the  raised  weight  until  it  is  liberated,  and  then 
this  force  comes  into  action  again  as  the  weight  comes 
down. 

In  the  same  way,  the  lifting  force  by  which  the  enormous 
quantity  of  vapor  in  the  atmosphere — millions  upon  mil- 
lions of  tuns  of  it — has  been  raised  to  the  altitude  which 
it  often  attains,  is  held  in  suspense,  as  it  were,  till  the  con- 
densation is  carried  so  far  as  to  set  the  water  free  to  de- 
scend, and  then  the  whole  of  it  is  given  out  again  in  the 
falling  rain. 

The  force  which  a  single  drop  of  water  exercises  in  mak- 
ing its  way  through  the  resistance  of  the  air,  and  in  finally 
striking  upon  the  ground,  seems  very  small,  but  the  aggre- 
gate of  this  force  in  the  rainfall  of  the  year  throughout 
the  globe  is  beyond  all  conception.  Some  estimate  of  the 
amount  of  water  which  the  atmosphere  contains  can  be 
made  by  examining  specimens  of  the  air  taken  from  a 
great  number  of  localities,  and  even  the  quantity  of  the 
rainfall  over  extensive  regions  may  be  ascertained  by  ob- 
servations made  in  different  places  within  the  bounds  of 
the  regions  to  be  examined,  for  it  is  easy  to  determine  the 


SELF-REGISTERING   INSTRUMENTS.  165 

amount  which  falls  in  any  one  spot  by  intercepting  and 
measuring  a  portion  of  it :  this  is  done  by  means  of  an  in- 
strument called  the  pluviameter. 

The  manner  in  which  the  more  simple  forms  of  the  plu- 
viameter are  made  and  used  has  been  explained  in  another 
volume  of  this  series.* 

There  has  been,  however,  very  great  improvement  in 
late  years  in  the  construction  of  all  instruments  for  making 
observations  on  the  phenomena  of  nature,  and  most  of  them 
now  are  made  automatic,  as  the  phrase  is — that  is,  self-act- 
ing. In  other  words,  strange  as  it  may  seem,  the  instru- 
ment makes  the  observation  and  records  the  result  without 
any  help  from  an  attendant.  Such  instruments  are  called 
sometimes  self -register  ing.  The  pluviameter,  for  instance, 
catches  the  water  falling  in  rain,  measures  it,  empties  the 
receptacle  when  it  is  full,  and  keeps  a  record  of  the  result. 
The  manner  in  which  this  is  done  is  shown  clearly  in  the 
engraving  on  the  following  page. 

In  the  upper  right  corner  of  the  apparatus,  GG  repre- 
sents a  sheet  of  paper  properly  ruled  and  extended  over  a 
board,  and  so  mounted  that  it  may  be  slowly  drawn  along 
in  an  equable  manner  by  means  of  the  weight  I,  the  de- 
scent of  which  is  regulated  by  the  clock-work  K.  The  rain 
is  caught  in  the  vessel  A,  which  is  placed  above  the  top  of 
the  building,  and  is  conveyed  by  the  pipe  BC  down  through 
the  roof  to  the  apparatus  DE  for  measuring  it ;  this  pipe, 
of  course,  is  longer  or  shorter,  as  the  case  requires,  as  is  in- 
dicated by  the  break  in  it  in  the  engraving  between  B  and 
C.  The  apparatus  for  receiving  and  measuring  the  rain, 
DE,  is  suspended  from  a  coiled  wire,  F,  which  acts  as  a 
spring,  and  allows  the  vessel  E  to  descend  in  proportion  as 
it  becomes  heavy  with  the  water  contained  in  it,  and  to 
rise  again  when  the  water  is  drawn  off.  At  the  lower  end 
*  HEAT,  Chapters  XI.  and  XII. 


166  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 


BELF-BEGISTERING  PLHVIA.METEK. 


of  this  spiral  spring  is  a  pencil,  which  is  drawn  up  and 
down  as  the  vessel  E  rises  and  falls,  and  thus  the  press- 
ing of  the  point  of  the  pencil  on  the  moving  sheet  of  paper 
records  all  the  changes  in  the  position  of  E  which  take 
place. 

Now  the  pipe  C  from  above  passes  through  the  spiral 
wire,  and  so  on  downward  into  the  vessel  E,  carrying  down 
and  delivering  there  the  rain  which  is  collected  by  the  re- 
ceptacle above.  Of  course,  as  the  vessel  becomes  heavy 


RECORDING  THE  RESULTS.  167 

from  the  rain  that  enters  it,  the  pencil  is  gradually  brought 
down,  and  as  the  paper  is  all  the  time  moving  forward  in 
the  direction  of  the  arrow,  it  traces  a  line  upon  the  paper 
inclining  downward  to  the  right,  the  degree  of  inclination 
being  shown  by  the  ruled  lines  on  the  paper. 

But  the  most  curious  part  of  the  apparatus  is  perhaps 
the  contrivance  for  emptying  the  vessel  when  it  has  be- 
come so  heavy  with  the  water  which  it  contains  as  to  bring 
down  the  pencil  to  the  bottom  of  the  sheet.  This  is  done 
by  a  siphon,  or  bent  tube,  placed  in  the  lower  part  of  the 
vessel.  The  water  will  not  flow  out  through  such  a  siphon 
unless  the  surface  of  it  has  risen  above  the  bend.  As  soon, 
however,  as  it  does  rise  to  this  height,  the  water  begins  to 
flow  rapidly  through  the  bend,  and  continues  to  flow  so 
until  the  vessel  is  emptied ;  this  is  done  almost  instantly, 
and  the  empty  vessel  is  then  at  once  drawn  up  again  by 
the  spring.  The  point  of  the  pencil,  in  rising,  makes  a  per- 
pendicular mark  from  below  upward,  and  then,  if  the  rain 
continues,  commences  a  new  record  of  the  progress  of  it 
by  a  new  inclined  line  downward  to  the  right  as  before. 

The  sheet  of  paper  is  so  regulated  as  to  its  movement  as 
to  be  twelve  hours  in  passing  the  point  of  the  pencil.  At 
the  end  of  that  time  there  is  made  upon  it  a  perfect  record 
of  the  rainfall  during  that  period.  It  is  then  taken  out 
and  filed  away,  and  its  place  is  supplied  by  a  new  one. 
Thus  the  lines  on  each  sheet  preserve  a  perfect  record  of 
the  amount  of  rainfall  for  twelve  hours,  the  horizontal 
lines  showing  the  time  during  which  no  rain  was  falling 
for  twelve  hours,  the  vertical  lines  from  below  upward 
showing  how  often  and  when  th'e  vessel  was  emptied,  and 
the  inclined  lines,  by  means  of  the  rulings  of  the  paper,  in- 
dicating at  what  rate  the  rain  fell  at  every  different  por- 
tion of  the  interval  between  them. 

This  engraving  represents  the  rain-measuring  apparatus 


168  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

in  use  at  the  observatory  in  the  Central  Park  at  New  York. 
It  has  been  in  operation  there  for  two  or  three  years,  and 
by  means  of  the  records  which  it  has  kept  it  can  at  once 
be  known  whether  or  not  it  was  raining,  and,  if  it  was  rain- 
ing, at  what  rate  the  rain  was  falling,  any  moment  during 
the  whole  of  that  period. 

Records  of  the  amount  of  the  rainfall  are  kept  in  a  great 
number  of  stations  at  the  present  day  in  all  parts  of  the 
world,  though  not  in  many  places  in  so  precise  and  detailed 
a  manner  as  by  the  system  just  described.  But  the  total 
amount  of  water  which  is  raised  from  the  earth's  surface 
by  the  power  of  the  sun,  acting  directly  and  indirectly 
upon  it,  and  then  allowed  to  fall  again,  is  enormous.  In 
the  case  of  the  Central  Park,  for  example,  the  quantity  of 
water,  in  the  form  of  rain  and  snow,  which  falls  in  one 
year  upon  the  Park,  is  sufficient,  if  it  could  be  retained 
where  it  falls,  to  cover  the  ground  to  a  uniform  depth  of 
about  three  and  a  half  feet.  Think  of  the  falling  force 
which  would  be  exercised  by  such  a  mass  of  water  as  this 
falling  at  once  from  the  height  of  the  clouds  to  the  ground  ! 
And  the  total  amount  of  the  force  is  the  same,  whether  it 
falls  in  one  moment  and  in  a  mass,  or  comes  in  drops,  and 
the  time  is  extended  to  a  year. 

And  we  can  obtain  a  more  vivid  idea  of  the  force,  too, 
by  supposing  it  to  be  a  thickness  of  three  and  a  half  feet 
of  solid  ice,  for  ice  of  the  same  weight  falls  no  more  heavi- 
ly, in  reality,  than  water.  The  falling  force  only  takes  ef- 
fect in  a  different  way,  the  force  with  which  the  water 
strikes  being  more  easily  divided  and  distributed,  and  the 
action  of  it  upon  the  ground  being  thus  less  obvious  to  the 
senses  than  that  which  would  be  manifested  by  the  same 
weight  in  a  solid  form. 

Mr.  H.  E.  Cole,  of  the  United  States  Signal  Service,  found 
that  the  quantity  of  water  which  fell  during  a  single  shower 


HEAT  SET  PEEE   BY   CONDENSATION.  169 

in  August  last  upon  the  city  of  Boston — an  area  of  about 
10,000  acres  —  from  Saturday  noon  to  Monday  morning, 
was  about  two  inches  by  measure,  and  amounted  in  weight 
to  more  than  two  millions  of  tuns !  and  yet  it  was  by  no 
means  an  exceptionally  copious  rain. 

He  also  estimated  that  the  amount  of  heat  set  free  in  the 
air  by  the  condensation  of  the  vapor  from  which  the  drops 
of  rain  were  derived  was  equivalent  to  that  which  would 
be  produced  by  the  combustion  of  over  a  hundred  and 
twenty  thousand  tons  of  anthracite  coal !  All  this  heat, 
moreover,  is  set  at  liberty  in  the  air,  not,  it  is  true,  in  a  con- 
centrated form,  as  it  would  be  if  produced  by  the  burning 
of  that  quantity  of  coal  in  a  furnace,  but  in  the  form  of  that 
low  degree  of  heat  which  would  appear  to  our  senses  only 
as  a  diminution  of  cold,  but  still  in  amount  the  same,  and 
effective  in  accomplishing  equivalent  results. 

And  all  this  heat  would  be  produced,  or,  rather,  given 
up  by  the  mere  condensation  of  the  vapors  from  which  the 
water  of  the  shower  was  derived.  There  is  the  falling 
force  of  that  immense  weight  of  water  besides,  though  this 
falling  force  is  converted  partly  into  heat,  which  is  ex- 
pended in  diminishing  the  cold  of  the  strata  of  air  through 
which  it  passes  in  its  descent,  and  partly  in  producing  a 
similar  effect  when  it  strikes  the  ground.  The  fall  of  rain 
has  thus  a  warming,  or,  rather,  a  cold-diminishing  tendency. 
This  tendency  is  often  very  perceptible  in  the  winter,  the 
formation  and  descent  of  rain,  or  even  of  snow,  being  usu- 
ally accompanied  by  a  diminution  of  the  intensity  of  the 
cold.  In  a  hot  summer's  day  the  effect  is  disguised  by  the 
rapid  evaporation  of  the  water  as  it  reaches  the  warm 
ground,  which  causes  it  suddenly  to  absorb  so  great  a  quan- 
tity of  heat  again  that  the  effect  at  the  surface  is  a  cooling 
one.  The  case  is  somewhat  analogous  to  that  above  de- 
scribed of  a  drop  of  warm  water  upon  the  hand. 
II 


170 


THE   FOUR   CIRCUITS    OF   SOLAK   ENERGY. 


It  is  only  a  small  part  of  the  falling  force,  however,  with 
which  the  rain  is  charged,  that  is  expended  when  it  strikes 
the  ground,  for  it  has  yet  usually  a  great  descent  to  make 
before  it  reaches  its  final  level  at  the  sea.  In  Boston,  it  is 
true,  this  remaining  portion  of  the  descent  is  small,  the  dis- 
tance being  but  a  few  feet ;  but  in  the  interior  of  the  coun- 


THE   PIN   MACHINE.  Ill 

try,  and  especially  in  mountainous  regions,  the  water  has 
often  a  descent  of  many  thousands  of  feet  yet  to  make,  and 
goes  on  expending  the  remaining  portion  of  its  falling  force 
as  it  flows  on  in  wearing  away  the  bank  of  its  channels,  or 
in  falling  with  great  momentum  over  lofty  precipices,  or 
tumbling  over  a  rocky  bed,  and  forming  long  cascades. 

When  men  have  work  to  be  done  in  which  this  portion 
of  the  falling  force  of  the  rain  can  be  profitably  employed, 
they  intercept  it  in  its  passage  by  dams,  and  draw  off  the 
force,  so  to  speak,  to  their  mills,  where  they  employ  it  in 
driving  their  saws,  working  their  looms,  or  turning  their 
spindles,  as  shown  more  fully  in  a  preceding  chapter.  And 
so  manageable  in  their  hands  this  force  is,  and  so  practi- 
cable is  it  for  them  to  divide  and  direct  it,  and  to  appro- 
priate it  to  the  purposes  they  require,  that,  by  means  of 
the  right  arrangement  of  machines,  it  can  be  made  to  man- 
ufacture a  pin  complete,  taking  the  wire  from  the  coil, 
straightening  it,  cutting  off  the  right  length,  fashioning  the 
head,  sharpening  the  point,  and  entirely  finishing  it,  with- 
out any  help  at  all  from  the  workman,  who  has  only  to 
stand  by  and  watch  the  process  as  it  goes  on.  Every  thing 
is  done  simply  by  the  falling  force  which  the  sun  has  stored 
in  the  water  in  raising  it  from  the  sea  into  the  air. 

It  is,  however,  but  a  small  part  of  the  force  exerted  by 
the  falling  water  from  the  atmosphere  that  is  utilized  by 
man.  It  is  true  that  there  are  tens  of  thousands  of  mills, 
and  pumping-engines,  and  factories  driven  by  it  in  differ- 
ent parts  of  the  earth,  but  then  there  are  hundreds  of  thou- 
sands of  streams  which  go  tumbling  down  the  mountain 
sides,  and  making  their  impetuous  way  along  ravines  and 
valleys,  expending  an  enormous  amount  offeree  in  modes 
wholly  independent  of  the  action  of  man. 


172  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 


CHAPTER  XL 

THE   FOUR    CIRCUITS    OF   SOLAR   ENERGY. 

3.  THROUGH  ICE  FORMATIONS. 

ICE  is  only  one  of  the  forms  of  water,  and,  scientifically 
speaking,  the  action  of  solar  force  in  its  connection  with 
the  formation  and  dissolution  of  ice  on  the  surface  of  the 
globe  might  properly  have  been  treated  in  the  last  chap- 
ter. But  the  nature  of  this  action,  or,  rather,  the  effects 
produced  by  it,  are  so  striking  and  peculiar,  that  they  de- 
serve to  be  treated  under  a  separate  head. 

We  have  seen  in  the  last  chapter  that  all  the  force  in 
the  form  of  heat  which  comes  from  the  sun,  and  enters  the 
air  and  water  upon  the  earth's  surface,  is  there  expended 
in  producing  a  variety  of  motions,  consisting  of  breezes, 
storms  and  tempests  in  the  air,  and  vast  currents  in  the 
sea,  and  in  raising  immense  weights  of  water  to  the  sky, 
and  letting  them  fall  again  with  great  force  to  the  earth ; 
and  the  question  at  once  arises,  What  ultimately  becomes 
of  all  the  force  thus  developed?  On  the  principle  hereto- 
fore laid  down  that  no  force  can  ever  be  lost,  Where  does 
this  force  go  ?  or,  rather,  What  becomes  of  it  in  the  end  ? 
Unless  it  is  disposed  of  in  some  way,  it  would  accumulate 
from  year  to  year,  and  from  century  to  century,  in  receiving 
continued  accessions  from  the  sun,  and  would  end  in  mak- 
ing great  and  permanent  changes  in  the  condition  of  things 
on  the  globe. 

But  no  such  change  takes  place — that  is,  no  great  and 
perceptible  change.  The  year  rolls  on ;  the  seasons  follow 


RADIATION   INTO   SPACE.  173 

each  other  in  regular  rotation ;  the  heat  and  cold  undergo 
fluctuations,  it  is  true,  to  a  certain  extent,  from  time  to 
time,  but  the  fluctuations  are  confined  within  comparative- 
ly narrow  limits;  the  course  of  change  returns  into  itself 
again  in  due  time,  and  every  thing  goes  on  substantially 
as  before.  Since,  then,  force  can  only  change  its  form,  but 
can  by  no  means  pass  out  of  existence,  what  becomes  in 
the  end  of  the  inconceivably  enormous  quantity  of  it  which 
falls  in  the  form  of  heat  every  day  of  every  year  upon  the 
surface  of  the  earth  from  the  sun  ? 

We  leave  out  of  the  question  at  present  that  portion  of 
the  solar  radiation  which  consists  of  light  and  of  actinic 
force,  and  consider  only  that  of  heat,  which  is  the  only 
portion  of  the  solar  radiation  with  which  we  have  thus  far 
been  dealing. 

The  answer  to  the  question  is,  that  this  heat,  after  pass- 
ing through  various  transformations  and  producing  a  vast 
variety  of  phenomena,  and  taking  many  different  forms,  is 
finally,  as  it  can  find  opportunity  when  the  influence  of  the 
sun  is  withdrawn,  radiated  away  again  beyond  the  earth's 
atmosphere  into  the  vast  regions  of  space  that  surround 
the  earth. 

That  is  to  say,  in  the  daytime  nnd  in  the  summer  the 
sun  pours  into  the  earth  floods  of  heat.  In  the  night  and 
in  winter  this  heat — substantially  the  whole  of  it — after 
passing  through  many  changes  of  form,  producing,  when 
turned  into  mechanical  force,  currents  in  the  water,  and 
winds  upon  the  land,  carrying  down  and  bearing  away 
vast  quantities  of  material  from  the  mountains  and  the 
plains,  undermining  and  grinding  down  the  rocks  along  the 
shores  of  the  sea,  and  driving  mills  and  machinery  in  vast 
numbers  for  the  benefit  of  man — goes  off  into  space  again, 
where  it  disappears  from  our  view.  What  finally  becomes 
of  it  is  at  present  an  unfathomable  mystery.  The  closest 


174  THE    FOUR  •  CIRCUITS    OF   SOLAR   ENERGY. 

scrutiny  of  science  has  not  yet  been  able  to  follow  it  into 
that  vast  store-house  of  cosmical  force  which  is  formed  by 
the  interstellar  regions,  or  to  discover  with  any  definite 
certainty  the  processes  by  which  it  is  ultimately  again 
concentrated  into  suns. 

There  will  be  something  more,  however,  to  be  said  on 
this  point  in  another  chapter. 

The  water,  then,  that  exists  on  and  near  the  surface  of 
the  globe,  exists  in  three  forms,  according  to  the  quantity 
of  heat  which  it  has  absorbed  from  the  sun.  In  its  lowest 
condition  'in  respect  to  heat,  it  is  ice.  It  is  reduced  to  this 
condition  whenever  it  has  radiated  into  space — either  di- 
rectly of  itself,  or  indirectly  through  other  substances — 
enough  heat  to  reduce  it  to  32°,  and  also  afterwai'd  a  quan- 
tity of  heat  equal  to  142  units  per  pound,  this  being  the 
"heat  of  liquefaction,"  so  called.  It  is  this  142  units  per 
pound  that  maintains  the  water  in  a  liquid  state  while  it 
continues  liquid ;  and  all  water  that  is  liquid  contains  this 
amount  of  heat  in  what  is  called  a  latent  condition,  em- 
ploying it  in  some  mysterious  way  in  maintaining  the 
liquidity. 

Now  the  water  which  is  in  the  polar  regions,  and  also 
in  the  temperate  regions  dui-ing  the  winter  when  the  sun 
is  away,  is  at  liberty  to  radiate  its  heat  into  space  very 
freely,  especially  at  night,  when  there  are  no  clouds  in  the 
sky  to  form  a  curtain  to  intercept  the  rays.  The  water, 
therefore,  in  immense  quantities,  in  all  these  regions,  loses 
its  heat  of  liquefaction  and  becomes  solid.  Wherever  the 
radiation  is  impeded  by  clouds,  or  whenever  the  water  is 
made  warm — in  the  sense  of  being  less  cold — by  friction, 
as  in  the  case  of  running  streams,  or  of  cataracts  falling 
over  rocks,  or  of  billows  surging  over  the  sea  or  being 
dashed  against  the  shore,  the  process  of  refrigeration  is 
hindered.  But  where  the  sky  is  clear,  and  the  water  is 


FORMATION  OP  ICE. 


175 


calm  and  still,  and  the  sun  is  away — that  is  to  say,  in  a  clear 
cold  night  in  the  winter,  and  even  in  the  daytime  when 
the  sun  is  low  in  the  horizon,  so  that  the  radiation  from 
the  sun  to  the  earth  is  partially  or  wholly  suspended,  while 
that  from  the  earth  into  space  can  go  on — then  the  water 
loses  gradually  its  heat  of  liquefaction  and  becomes  solid. 

And  this  is  the  philosophy  of  the  formation  of  ice  in  the 
high  latitudes. 

This  process,  however,  does  not  go  on  in  any  uniform  or 
continuous  manner,  but  fitfully  and  with  great  fluctuations. 
Throughout  vast  portions  of  those  parts  of  the  earth's  sur- 


OONTENDINQ   RADIATIONS. 


176  THE    FOUR   CIRCUITS   OF   SOLAR   ENERGY. 

face  a  constant  contest  is  going  on  between  the  radiation 
from  the  earth,  abstracting  heat  from  the  terrestrial  waters, 
and  that  from  the  sun  counteracting  the  loss.  The  charac- 
ter of  this  conflict  is  well  illustrated  in  the  engraving  rep- 
resenting a  scene  in  Spitsbergen,  where  the  sun  has  very 
little  power,  the  radiation  of  heat  from  the  earth  tending 
to  condense  the  vapors  in  the  air,  and  to  solidify  the  water 
on  the  sea.  But  the  feeble  radiation  of  the  sun  maintains 
an  unequal  and  doubtful  contest  with  it,  yet  so  far  prevails, 
at  the  time  and  under  the  circumstances  represented  in  the 
engraving,  as  to  prevent  such  an  amount  of  condensation 
in  the  vapor  as  would  produce  copious  rain,  and  to  limit 
the  formation  of  ice  upon  the  surface  of  the  sea. 

Far  to  the  north  or  south,  in  the  arctic  and  antarctic 
regions,  the  influence  of  the  sun  is  so  feeble,  especially 
through  the  winter  portion  of  the  year,  that  the  heat  radi- 
ated and  lost  in  space  during  the  cold  season  is  not  re- 
placed during  the  summer,  and  the  ice  accumulates.  All 
the  vapors  in  the  atmosphere  which  find  their  way  thither, 
after  having  been  raised  from  the  sea  in  more  genial  climes, 
lose  their  heat,  both  of  vaporization  and  liquefaction,  and 
are  condensed  in  the  air  into  snow.  Or,  if  the  radiation  of 
the  stored  heat  is  more  slow,  so  that  the  moisture  falls  in 
rain,  it  loses  its  heat  of  liquefaction  as  soon  as  it  comes  in 
contact  with  the  intensely  cold  surfaces  that  receives  it — 
that  is,  it  freezes  as  it  falls — and  forms  with  the  snow  that 
has  previously  fallen  beds  of  ice  of  great  thickness  and 
solidity;  and  as  there  is  very  little  melting  of  the  mass 
during  the  summer,  the  depth  of  the  accumulation  increases 
from  age  to  age,  until  glaciers  are  formed  hundreds  and 
sometimes  thousands  of  feet  in  thickness. 

Here  it  would  i*emain,  increasing  in  depth  indefinitely, 
were  it  not  for  one  most  extraordinary  action  to  which 
such  accumulations  of  ice  are  subject,  and  that  is,  that, 


GLACIERS.  17? 

however  gentle  the  incline  of  the  surface  on  which  they 
lie,  they  are  subject  to  a  slow  creeping  motion  down  the 
slope  toward  the  sea.  And,  what  is  still  more  wonderful, 
even  when  such  a  glacier  fills  a  tortuous  valley  bordered 
by  steep  and  ragged  rocks  on  each  side,  the  enormous  fric- 
tion of  the  sides  is  not  sufficient  to  hold  it.  It  moves  slow- 
ly onward  in  summer  and  in  winter,  by  night  and  by  day, 
at  the  rate  of  a  few  inches  in  twenty-four  hours — the  rate 
varying,  however,  with  the  temperature  and  other  circum- 
stances— until  at  length  it  reaches  the  shore  of  the  sea. 

The  movement  of  such  glaciers  has  been  studied  more 
in  Switzerland  than  in  any  other  country,  and  a  long  time 
elapsed,  and  many  exact  observations  were  made,  before 
mankind  could  be  satisfied  that  masses  of  such  apparent 
solidity,  and  so  firmly  held  in  their  rocky  beds,  could  real- 
ly move.  But  the  proof  soon  became  overwhelming.  In 
Switzerland  the  glaciers  generally  lie  in  vast  ravines  and 
valleys  among  the  mountains,  and  they  gradually  work 
their  way  down  to  the  warmer  valleys  below,  where  the 
ice  at  the  terminus  is  melted  by  the  sun.  But  in  Green- 
land and  in  other  polar  regions  such  formations  of  ice  cover 
extended  tracts  of  country  like  a  vast  bed  of  rock,  and 
move  slowly  down  till  they  reach  the  sea.  Then  and  there 
the  margin,  crowded  onward  by  the  mass  behind,  protrudes 
over  the  water,  till  immense  masses  of  if  are  broken  off  and 
floated  away.  And  this  is  the  origin  of  the  icebergs  float- 
ing in  the  sea,  which  so  often  attract  the  attention  of  voy- 
agers in  crossing  the  Atlantic. 

Besides  these  mountains  of  ice,  formed  upon  the  land 
and  floated  off  by  the  waves,  vast  sheets  of  solidified  water 
are  formed  in  certain  seasons  over  the  surface  of  the  sea, 
while  the  sun  is  away,  and  in  places  where  the  water  is 
not  kept  warm — that  is,  kept  from  giving  up  the  large 
quantity  of  heat  which  must  be  abstracted  from  it  to  bring 
H  2 


178 


THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 


it  from  a  liquid  to  a  solid  state — by  the  incessant  turmoil 
of  the  waves.  Ice  thus  formed  is  called  field  ice.  It  is 
sometimes  from  six  to  ten  feet  in  thickness,  and  often  vast 
tracts  of  it  become  detached  from  the  shores  of  the  shel- 
tered waters  where  it  is  formed,  and  are  floated  away  by 
the  currents  or  driven  by  the  winds  out  to  the  open  sea,  to 
be  finally  broken  to  pieces  by  the  agitation  of  the  waves. 


FIELD   IOB. 


The  remains  of  the  icebergs  and  the  fragments  of  the 
field  ice  are  borne  by  the  currents  sometimes  a  thousand 
miles  or  more  from  the  places  of  their  origin.  It  is  often 
a  matter  of  surprise  to  the  voyagers  that  encounter  them 
that  they  melt  so  slowly  and  endure  so  long,  just  as  peo- 
ple who  do  not  reflect  upon  the  subject  are  often  surprised 
that  a  piece  of  ice  should  be  so  slow  in  melting  in  a  glass 
of  water  in  a  summer's  day.  The  glass  of  another  tumbler, 
forming  a  mass  much  greater  than  the  lump  of  ice,  is 


COOLING    EFFECT   OF   ICE.  179 

warmed  in  a  few  minutes  when  tepid  water  is  poured  into 
it,  while  the  ice  in  a  similar  quantity  of  water  of  the  same 
temperature  parts  with  its  cold — that  is,  is  affected  by  the 
surrounding  heat — very  slowly,  for  portions  of  it  remain  in 
the  condition  of  ice  for  a  long  time. 

The  reason  is,  that  the  glass  employs,  so  to  speak,  all  the 
heat  which  it  receives  iu  simply  warming  itself.  It  uses 
none  of  it  to  change  its  internal  constitution  from  the  solid 
to  the  liquid  form.  Every  unit  of  heat  which  the  water 
passes  into  the  glass  w.arms  it  at  the  rate  of  one  degree 
per  pound.  But  in  regard  to  the  ice  the  case  is  different. 
The  large  quantity  of  142  units  of  heat  per  pound  must  be 
employed  in  melting  the  ice ;  that  is  to  say,  this  great 
amount  must  pass  into  a  latent  condition,  and  so  disappear 
from  observation,  in  the  work  of  liquefying  the  ice,  before 
any  of  it  will  be  employed  in  warming  the  liquid  that  re- 
sults. This  is  the  reason  why  the  ice  melts  so  slowly,  and 
why,  consequently,  icebergs  and  fields  of  ice  endure  so  long 
into  the  summer  in  the  comparatively  warm  waters  of  the 
mid-Atlantic,  and  why  a  lump  of  ice  will  keep  the  water 
cooler  in  a  tumbler  so  much  longer  than  a  cold  stone,  as 
large  and  as  cold  as  itself,  would  keep  it. 

We  have  now  to  consider  a  very  striking  and  important 
difference  which  results  in  the  effects  produced  by  a  portion 
of  the  heat  of  the  sun  which  is  employed  in  liquefying  ice 
from  that  which  expends  its  energy  in  vaporizing  water. 

The  difference  is  this,  that  whereas,  when  water  is 
changed  from  the  liquid  to  the  vaporous  form,  it  goes  up, 
while,  on  the  other  hand,  when  it  is  changed  from  the  solid 
to  the  liquid  form  by  the  same  agency,  it  sends  the  result- 
ing currents  down. 

Thus  the  vapors  produced  by  the  heat  of  the  sun  ascend 
and  float  over  the  surrounding  air.  The  water  from  a  float- 


180  THE    FOUR   CIRCUITS    OF   SOLAE    ENERGY. 

ing  iceberg  sinks  and  flows  away  underneath  the  other 
water  at  the  bottom  of  the  sea. 

The  reason  is  that  water,  in  freezing,  swells,  so  that  a 
mass  of  ice  is  lighter  than  the  water  out  of  which  it  was 
formed.  Warm  water,  too,  is  lighter  than  cold  water,  for 
it  is  only  just  before  it  freezes,  and  while  it  is  freezing, 
that  it  swells.  Before  that  time  it  swells  as  it  becomes 
warm,  and  diminishes  in  bulk  as  it  grows  cold.  Thus,  if 
we  have  water  only  in  a  sea,  or  in  a  tumbler,  or  in  a  re- 
ceptacle of  any  kind,  the  warmest  portion  of  it  will  tend 
to  be  at  the  top,  and  the  coldest  of  it  within  certain  limits 
at  the  bottom — that  is,  so  long  as  there  is  none  cold  enough 
to  be  ready  to  begin  to  freeze.  As  soon  as  any  portion  of 
it  approaches  the  freezing  point,  it  rises  to  the  surface  and 
freezes  there,  and  after  it  is  frozen  it  remains  upon  the 
surface  until  it  is  melted  again.  Then,  and  only  then,  it 
goes  down. 

The  icebergs,  as  has  already  been  said,  are  formed  gen- 
erally on  the  land  in  Greenland  arid  Spitzbergen,  and  in 
other  arctic  and  antarctic  countries.  They  are  formed  by 
the  gradual  accumulation  and  consolidation  of  the  snows 
over  a  great  extent  of  country,  the  whole  formation  work- 
ing slowly  all  the  time  onward  toward  the  sea;  and  as  the 
immense  mass  reaches  the  sea,  and  portions  of  it  are  broken 
o.T  and  borne  away  by  the  floating  power  of  the  water, 
they,  of  course,  are  lighter  than  the  water,  and  keep  at  the 
top,  where  the  warmth  of  the  water  lies.  Thus,  in  a  sea 
covered  more  or  less  with  floating  ice,  we  have  the  coldest 
— that  is,  the  ice — and  also  the  warmest — that  is,  the  water 
which  has  been  moderated  in  temperature  by  the  sun — 
upon  the  top,  while  the  coldest  liquid  water  lies  motionless, 
or  flows  in  a  slow  current  in  the  depths  below. 

And  as  fast  as  the  ice  is  melted  by  the  sun,  or  by  the 
warmth  which  it  absorbs  from  the  surrounding  water,  a 


EFFECT   OF   THE   SALTNESS.  181 

mass  of  cold  water  results,  both  from  the  liquefaction  of 
its  own  substance,  and  also  from  its  cooling  effect  upon  the 
liquid  lying  around  it.  This  cold  water  descends  continu- 
ally, as  fast  as  it  is  produced,  in  vertical  currents,  until  it 
reaches  the  level,  in  the  vast  underflow,  where  the  temper- 
ature and  the  density  corresponds  with  its  own. 

It  is  true,  the  process  is  in  some  degree  complicated,  and 
that  the  direct  results  are  modified  by  the  saltness  of  the 
sea ;  for  salt  water  is  heavier  than  fresh,  on  account  of 
the  weight  of  the  salt  which  it  contains ;  consequently,  a 
body  of  fresh  water,  even  though  somewhat  colder  than 
the  salt  water  in  which  it  was  lying,  might  float  upon  or 
near  the  surface  of  it.  It  is  also  true  that,  for  some  myste- 
rious reason,  when  ice,  on  losing  its  heat  of  liquefaction,  be- 
comes water  at  32°,  it  is  not  quite  at  its  maximum  density. 
Its  maximum  density  is  at  about  40°.  It  follows,  from  the 
operation  of  both  these  causes  combined,  that  if  an  iceberg 
could  be  simply  melted,  and  if  the  water  resulting  from  it 
could  be  kept  distinct  from  the  sea  water  around  it,  it 
would  form  a  floating  mass  to  remain  on  the  surface.  But, 
in  fact,  the  water  thus  produced  soon  becomes  so  mingled 
with  the  sea  water  that  it  acquires  from  it  a  portion  of  its 
saltness,  and  also  of  its  cold — that  is,  it  absorbs  from  it  so 
much  heat  that  the  compound  mass  becomes  heavier  than 
the  water  of  the  surrounding  sea,  and,  as  fast  as  it  thus  be- 
comes heavier,  it  goes  down.  Thus,  while  the  vapors  pro- 
duced by  heat  from  liquid  water  go  up,  the  liquid  pro- 
duced in  the  same  way  from  solid  water  goes  doicn. 

The  result  is  that,  as  a  general  truth,  there  is  a  stratum 
of  comparatively  warm  water  flowing  in  a  thousand  cur- 
rents over  the  surface  of  the  sea,  and  a  vast  bed  of  colder 
water  moving  slowly  in  a  contrary  direction  far  below,  the 
general  tendency  of  the  warm  water  being  from  the  warm 
regions  of  the  earth  toward  the  colder  ones,  and  of  the 


182  THE   FOUR   CIRCUITS   OP   SOLAR   ENERGY. 

cold  water  from  the  colder  regions  to  the  warmest  ones; 
these  general  movements,  however,  being  modified,  and 
changed,  and  disturbed  in  a  thousand  ways  by  the  action 
of  the  winds,  the  formation  of  eddies,  the  trend  of  coasts, 
and  a  multitude  of  other  disturbing  causes. 

If  ever,  then,  the  reader  crosses  the  Atlantic,  and  looks 
out  from  the  deck  of  his  vessel  to  a  sea  covered  in  part 
with  icebergs  and  ice  floes,  he  must  picture  to  his  imagina- 
tion, first,  a  vast  general  movement  of  the  surface  water 
toward  the  north;  secondly,  an  equal  movement  toward 
the  south  of  an  immense  body  of  colder  water  in  the  depth 
below;  and,  thirdly,  a  countless  number  of  vertical  streams 
from  every  iceberg  and  floe,  formed  by  the  cold  water  re- 
sulting from  the  melting  of  the  ice,  flowing  downward^  hun- 
dreds of  fathoms,  from  the  upper  currents  to  the  under  one. 

The  general  rule  of  the  flow  of  the  warm  water  on  the 
surface  toward  the  poles,  and  of  cold  water  from  the  poles 
toward  the  equator,  is  subject,  as  has  already  been  said,  to 
a  great  many  modifications  and  exceptions,  arising  from 
the  action  of  local  causes.  The  northward  flow,  for  exam- 
ple, of  the  warm  water  in  the  Atlantic  Ocean  is  greatly  in- 
tensified within  certain  limits,  forming  what  is  called  the 
Gulf  Sti-eam,  and,  on  the  other  hand,  within  certain  other 
limits,  commencing  in  Baffin's  Bay,  and  so  coming  down  on 
the  eastern  coast  of  North  America,  something  like  a  vast 
eddy  is  formed,  and  the  set  of  the  surface  water,  though 
cold  and  full  of  icebergs  and  floes,  is  toward  the  south. 
The  result  is,  that  an  immense  quantity  of  floating  ice  is 
brought  down  from  the  extreme  northern  regions  by  the 
currents,  and  carried  around  the  northeastern  coast  of  New- 
foundland, and  thus  drifted  out  into  the  middle  of  the  At- 
lantic, where  it  encounters  the  northern  flow  of  the  warmer 
water,  and  is  rapidly  melted.  The  encounter  of  this  quan- 
tity of  ice  and  ice-cold  water  with  the  warmer  waters  from 


EQUALIZING   EFFECTS.  183 

the  south  results  in  a  condensation  of  the  vapors  in  the 
air  so  great  and  so  extended  as  to  cover  the  surface  of  the 
sea,  and  envelop  all  the  coasts,  in  certain  seasons  of  the 
year,  with  fogs,  and  mists,  and  scudding  clouds,  and  driving 
rain,  which  make  the  navigation  fearful  to  the  mariner. 

Thus,  to  sum  up  the  whole  process  in  one  word,  the  radia- 
tion of  the  terrestrial  heat  from  the  earth,  in  the  vicinity 
of  the  poles,  deprives  the  water  there  of  its  heat  of  lique- 
faction, and  forms  vast  quantities  of  ice,  which,  as  long  as 
the  masses  are  held  in  place,  remain  unchanged  from  age 
to  age ;  but,  as  soon  as  they  become  detached  from  their 
places  and  are  set  at  liberty,  they  come  at  once  under 
the  control  of  winds  and  currents,  and,  though  the  general 
set  of  the  surface  currents  is  toward  the  pole  in  all  these 
waters,  a  vast  number  of  the  liberated  masses  are  brought 
under  the  influence  of  counter  currents  and  of  winds,  which 
bring  them  down,  after  many  stops  and  much  floating  to 
and  fro,  to  warmer  climes. 

They  greatly  assist  in  this  way  in  equalizing  the  tem- 
perature of  the  earth,  or,  rather,  in  promoting  a  tendency 
to  equalization  in  it.  Icebergs  and  ice  floes,  by  the  very 
process  of  their  formation,  must  tend  to  make  the  polar 
regions  that  produce  them  less  cold  than  they  otherwise 
would  be ;  for  ice  can  not  be  formed  without  having  the 
heat  of  liquefaction  taken  out  of  the  water  from  which  it 
is  formed,  and  there  is  no  way  by  which  this  heat  can  be 
taken  out  except  by  the  surrounding  bodies,  or  the  sur- 
rounding space,  receiving  it.  And  then,  by  their  dissolu- 
tion, they  must  make  the  tropical  regions  less  warm;  for 
they  can  only  be  dissolved  by  absorbing  heat  to  supply  that 
which  was  lost  in  the  freezing,  and  the  heat  thus  required 
the  surrounding  objects,  or  the  surrounding  space,  must 
render,  and  must  cool  themselves  somewhat  in  doing  it. 

It  is  thus,  by  the  processes  described  in  this  and  the  pre- 


184  THE   FOUR   CIRCUITS    OP   SOLAR    ENERGY. 

ceding  chapter,  that  a  large  portion  of  the  solar  foi'ce  which 
consists  of  heat  is  distributed  through  the  medium  of  water, 
in  its  different  forms,  very  extensively  over  the  surface  of 
the  globe.  It  is  received  from  the  sun  in  its  greatest 
intensity  in  the  tropical  regions,  and  in  a  constantly  di- 
minishing ratio  from  those  regions  to  the  poles.  As  we 
observe  its  progress,  we  see  it  pursuing  its  devious  and 
meandering  way  through  the  atmosphere  and  over  the  sea, 
moving  in  its  course  through  a  thousand  changes,  forming 
currents  and  counter  currents,  and  eddies  innumerable; 
sometimes  advancing  through  the  ocean  in  a  majestic 
stream,  and  at  others  receding  in  an  equally  vast  reflex, 
revolving  in  whirlpools  and  tornadoes,  beaten  back  from 
rocky  coasts,  rising  in  vapors,  and  descending  in  snow,  hail, 
and  rain,  but  still,  on  the  whole,  gradually  making  prog- 
ress from  the  equatorial  toward  the  polar  regions,  and  also 
stealing  off  continually  by  the  way,  until,  in  the  end,  it 
has  all  escaped  from  the  earth  by  radiating  into  the  re- 
gions of  infinite  space,  where  we  can  follow  it  no  farther ; 
the  last  portions  of  it,  taking  their  departure  from  the  earth 
at  the  polar  regions,  and  leaving  behind  them  icebergs  and 
ice  floes  to  be  sent  back  for  new  supplies. 

For  the  icebergs  may  be  considered  in  some  sense  as 
empty  vehicles  of  transportation,  going  back  to  be  charged 
anew  with  supplies  of  heat,  which  are  to  be  brought  from 
the  tropics  to  the  poles.  In  being  formed  into  ice,  the 
water  which  composes  them  gave  out,  as  we  have  seen,  its 
supply  of  heat,  especially  the  142  units  per  pound  which 
had  before  maintained  them  in  the  condition  of  liquidity. 
As  they  move  south  they  voraciously  seek  to  recover  this 
supply.  They  seize  it  from  any  of  the  water  that  they 
meet  which  is  able  to  supply  them.  When  they  thus  be- 
come liquid  again,  they  join  the  other  streams  of  cold  water 
flowing,  in  the  main,  toward  the  south,  and  sooner  or  later 


EFFECTS  OF   THE  AVAI.ANOHE. 


FORMATION    OP   PEAKS.  187 

they  become  warm  enough  to  take  their  turn  in  flowing 
north  again  as  warm  and  liquid  water  on  the  surface  of 
the  sea,  or  to  be  raised  as  vapor  into  the  air,  and  to  be 
wafted  by  the  winds  where  the  heat  that  they  have  now 
recovered  again  is  most  required. 

A  very  considerable  portion  of  the  heat  which  finds  its 
way  in  these  channels  of  circulation  takes  effect,  as  me- 
chanical  force,  in  forming  currents,  and  driving  icebergs 
and  fields  of  ice  to  and  fro  with  enormous  momentum. 
The  ice  acts,  in  fact,  not  merely  by  the  grinding  effect  of 
great  floating  masses  driven  by  the  winds  into  the  bays 
and  against  the  rocks  of  the  coast,  but  also  by  the  slow 
but  immensely  powerful  action  of  the  glaciers  in  valleys 
of  the  interior.  Ice  also  acts  sometimes  in  another  very 
striking  manner  by  forming  a  solid  covering  on  the  sides 
of  a  mountain  or  hill,  and  afterward,  by  its  fall  in  ava- 
lanches, carrying  away  portions  of  the  declivity  with  it. 

In  this  way  it  gradually  increases  the  precipitousness  of 
the  mountain  sides,  and  in  the  end  forms  rugged  and  barren 
peaks  of  extraordinary  picturesqueness  and  grandeur. 

When  this  action  of  the  ice  takes  place  on  the  sea-shore, 
so  that  it  is  conjoined  with  the  undermining  and  abrading 
influence  of  the  waves,  the  result  is  greatly  to  modify  the 
configuration  of  the  coast  and  the  character  of  the  scenery ; 
and,  inasmuch  as  the  land  every  where  throughout  the 
globe  is  subject  to  great  alterations  of  level,  and  to  great 
changes  in  respect  to  heat  in  different  seasons,  and  in  dif- 
ferent ages  of  the  world,  it  is  often  difficult  to  determine, 
in  respect  to  any  scenery  which  presents  wild,  broken,  and 
rugged  features  to  the  view,  whether  the  agency  of  ice 
may  or  may  not  have  been  employed  in  some  former  pe- 
riods in  producing  the  forms  which  now  characterize  it  so 
strongly. 

Notwithstanding  the  intense  cold  which  prevails  in  the 


188  THE   FOUR   CIRCUITS   OP   SOLAR   ENERGY. 


60ENEBY  ON   T1IE  COAST  OP  NORWAY. 


arctic  and  antarctic  regions,  and  the  violent  action,  so  in- 
cessant and  so  destructive,  of  the  various  ice  formations, 
such  as  the  glaciers  on  the  land,  and  the  floating  icefields 
and  icebergs  on  the  sea,  there  is,  perhaps,  no  region  on  the 
earth  more  profuse  in  the  productions  of  organic  life.  Low 
forms  of  vegetable  and  animal  existence  swarm  in  the  seas. 
These  favor  the  growth  and  propagation  of  innumerable 
shoals  of  fishes  and  other  marine  animals  that  are  enabled 
to  bear  the  cold  by  being  endowed  with  an  organization 
that  is  satisfied  with  maintaining  in  their  bodies  a  tem- 
perature only  slightly,  if  at  all,  elevated  above  that  of  the 
water  in  which  they  swim.  A  higher  order  of  animals,  re- 
quiring a  higher  temperature  to  keep  their  organs  in  play, 


HEAT   PRESERVERS. 


189 


multiply  upon  and  around  the  icy  shores  by  feeding  upon 
the  fishes — whales,  seals,  and  walruses  in  the  sea,  gulls  and 
other  birds  of  prey,  in  countless  millions,  in  the  air,  and 
bears,  foxes,  and  reindeer  upon  the  ice.  These  all,  requir- 
ing, as  they  do,  for  their  high  organization,  a  supply  of 
warm  blood  in  their  veins,  are  provided  both  with  the 
means  within  of  rapidly  developing  heat  from  their  food, 
and  also  of  preserving  what  they  thus  evolve  by  means  of 
a  special  provision  in  each  class — feathers  for  the  birds, 


AMONG  TUB   ICEBF.KG8  AFTEE  SEALS  AND   W11ALES. 


190  THE    FOUK   CIRCUITS    OF   SOLAR   ENERGY. 

furs  for  the  land  animals,  and  thick  coats  of  blubber  and 
oil  for  those  that  find  their  home  in  the  sea. 

And,  finally,  as  these  different  grades  of  animals  prey 
upon  each  other  in  regular  succession,  the  elements  of  sus- 
tenance passing  up  from  the  lowest  to  the  highest  as  the 
exigencies  of  each  rank  require,  man  comes  in  at  last  to 
prey  upon  the  highest  of  them,  these  elements  having  then 
taken  the  form  adapted  to  his  use.  It  is  the  feathers,  the 
furs,  and  the  oil,  as  means  of  protection  for  him  from  cold 
and  darkness,  which  draw  him  to  the  spot.  He  comes  in 
search  mainly  of  the  seals  and  the  whales,  for  the  sake  of 
the  light  and  the  warmth  which  he  can  procure  for  himself 
from  the  constituents  of  their  clothing. 

Perhaps,  however,  the  most  wonderful  fact  connected 
with  the  wrorld  of  vital  activity  to  be  witnessed  in  these 
regions  is,  that  all  the  force  that  is  manifested  in  it,  like 
that  which  is  exercised  by  the  waves  and  currents  of  the 
sea,  the  fall  of  water  on  the  land,  the  crashing  impetus  of 
fields  and  mountains  of  ice,  and  the  violence  of  hurricanes 
and  tornadoes,  is  derived  solely,  though  more  or  less  di- 
rectly, from  the  radiation  of  the  sun. 

And  this  brings  us  to  the  subject  of  the  next  chapter, 
which  is  to  treat  of  the  fourth  circuit  of  solar  energy, 
namely,  the  course  it  follows,  and  the  effects  which  it  pro- 
duces by  its  action  in  and  through  the  organs  of  vegetable 
and  animal  life. 


VEGETABLE   AND   ANIMAL  LIFE.  191 


CHAPTER  XIL 

THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

4.  THROUGH  THE  ORGANS  OF  VEGETABLE  AND  ANIMAL 
LIFE. 

THERE  are  many  very  curious  analogies  to  be  observed 
lii  comparing  the  phenomena  of  vegetable  and  animal  life, 
both  in  respect  to  structure  and  function,  especially  in  the 
lower  forms  of  the  organizations  that  we  observe.  Indeed, 
iu  these  lower  forms  the  two  principles  seem  almost  to 
blend  into  one,  and  it  has  been  found  difficult  to  draw  pre- 
cisely the  line  of  demarkation  which  separates  them.  In 
their  relation  to  force,  however,  the  distinction  between 
plants  and  animals  seems  broad  and  clear.  In  fact,  in  this 
respect  they  are  antithetical  and  complementary  to  each 
other;  for 

It  is  essentially  the  function  of  vegetable  life  to  col- 
lect, absorb,  and  store  the  energy  that  comes  from  the  sun, 
and  that  of  the  animal  organization  to  appropriate  and  ex- 
pend it. 

It  is  true  there  is  a  great  deal  of  expenditure  offeree  to 
be  observed  in  connection  with  the  vegetable  organization, 
but  it  is  all  incidental,  and  there  may  be  also  more  or  less 
of  the  direct  absorption  of  solar  energy  by  the  animal  or- 
ganization, but  this,  too,  is  incidental.  The  primary  object 
of  the  organs  of  the  one  is  to  absorb  the  force  to  be  de- 
rived from  the  solar  radiation,  and  that  of  the  other  to  re- 
ceive the  force  so  made  ready  for  it,  and  to  expend  it,  and 
thus  set  it  free  again. 


192  THE    FOUR   CIRCUITS    OF   SOLAR    ENERGY. 

In  the  lower  forms  of  animal  and  vegetable  life  these 
two  functions  may  possibly  be  found,  it  is  true,  to  be  united 
in  the  same  organization ;  but  in  all  the  higher  forms,  and 
even  in  the  lower,  so  far  as  they  have  yet  been  fully  ob- 
served, the  distinction  is  clear. 

Thus  the  grass  in  the  field  collects  the  radiant  solar  en- 
ergy, stores  it  in  its  leaves,  its  stems,  its  flowers,  and  espe- 
cially iu  its  seeds.  The  ox  receives  it  thus  prepared  for 
him,  and  expends  it  in  plowing  fields,  and  drawing  loads, 
and  exercising  and  expending  mechanical  force  in  other 
ways,  for  his  own  benefit  or  for  that  of  man. 

The  flower-bearing  plants  of  the  field  are  busy  during 
the  long  summer  mornings  in  laying  up  force  from  the  sun 
in  their  juices.  The  insect  comes  and  receives  the  stores 
of  force  thus  prepared,  and  expends  a  portion  of  it  in  his 
motions  to  and  fro,  whether  of  creeping,  of  leaping,  or  of 
flight,  in  his  combats  with  his  enemies  or  his  prey,  and  in 
the  industrial  labor  which  he  employs  in  excavating  his 
hole,  or  building  his  nest,  or  spinning  his  web  or  cocoon. 
In  some  cases,  as  in  that  of  the  bee,  he  stores  away  a  por- 
tion of  this  for  future  use  in  the  form — or,  rather,  in  the 
chemical  constitution — of  certain  substances  which  he  pro- 
duces, such  as  wax  and  honey ;  and  this  reserved  supply 
is  afterward  appropriated  and  brought  into  action  either 
by  himself,  when  he  uses  it  for  fgad  at  a  later  period,  or  by 
the  bear  or  the  man  who  plunders  his  hive. 

What  we  have  to  consider  in  this  chapter  is  the  man- 
ner in  which  the  solar  force  is  thus  absorbed  and  concen- 
trated in  plants,  and  afterward  appropriated  and  expended 
by  animals ;  in  other  words,  to  consider  the  fourth  branch 
of  the  subject  of  solar  energy,  namely,  its  circuit  through 
the  organs  of  vegetable  and  animal  life. 

The  apparatus  by  means  of  which  the  appropriation 
and  the  storage  of  solar  force  are  secured  in  plants  is 


VEGETABLE    OKGANS. 


193 


found  by  the  microscope  to 
be  wonderfully  complicated 
and  curious.  All  over  the 
surface  of  the  leaves  are 
found  small  openings,  called 
stomata,  from  the  Grk.  word 
?toma,  meaning  a  mouth. 
These  openings  lead  to  "  in- 
tercellular cavities  in  the 
subjacent  tissue,"  into  which 
the  carbonic  acid  gas  and  the 
aqueous  vapor  of  the  atmos-  Fig.  I.-STOMATA. 

phere  are  received ;  and  here,  in  some  way  or  other,  the 
solar  force  takes  effect  in  separating  them  into  their  ele- 
ments of  carbon  and  hydrogen  on  the  one  hand,  and  oxy- 
gen on  the  other.  The  carbon  and  hydrogen  the  plant  re- 
serves and  builds  into  its  tissues,  while  it  sets  the  oxygen 
free.  The  elements,  thus  separated  from  each  by  the  over- 
powering force  of  the  sun,  retain  their  immensely  strong 
affinity  for  each  other,  and  this  affinity  is  ready  at  all  times 
to  come  into  action  again  whenever  the  conditions  favor- 
able for  such  reunion  shall  be  attained. 

i^  In  Fi<r.  2  we  have  a 

jonnr 


sectional  view  of  a  stoma, 
showing  its  connections 
with  the  interior  tissue. 
The  stomata  are  alto- 
Fig.  2._8ECTio*  OF  A  STOUA.  gether  too   minute,  in 
most  plants,  to  be  seen  by  the  naked  eye. 

We  have  already  seen  in  a  former  chapter  that  when  a 
weight  is  raised  above  the  surface  of  the  earth,  the  force 
which  is  expended  in  raising  it  is,  in  a  certain  sense,  stored 
in  it,  and  retained  until  the  weight  is  released,  and  that 
then,  in  coming  down,  it  exercises  precisely  that  degree  of 
I 


194  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

force  in  its  descent,  neither  less  nor  more,  which  was  ex- 
pended in  raising  it ;  and  that  the  force  so  liberated  may 
be  applied  to  any  purpose  for  which  man  may  wish  to  ap- 
ply it,  and  must  necessarily  be  expended  in  producing  some 
effect  or  other. 

Now  it  seems  that  there  is  an  up  and  a  down — or  some* 
thing  strikingly  analogous  to  this — in  the  chemical  consti- 
tution of  bodies — that  is  to  say,  that  a  certain  change  may 
be  produced  in  the  relation  of  the  particles  to  each  other 
by  the  application  of  force  —  as  in  the  ease  above  de- 
scribed, of  carbon  and  hydrogen  on  the  one  hand,  and  oxy- 
gen on  the  other — which  is  such  that  when  they  are  re- 
leased from  the  constraint,  and  certain  t>ther  conditions 
favor,  they  tend  to  restore  themselves  to  the  former  state ; 
and  what  is  most  remarkable,  and  most  important  to  be  un- 
derstood and  remembered  is,  that  in  thus  restoring  them- 
selves, they  give  back,  in  returning  to  their  former  condi- 
tion, precisely  the  same  amount  of  force  as  that  which  was 
expended  in  producing  the  original  change;  and,  moreover, 
that  this  force,  thus  released,  may  be  applied  to  any  pur- 
pose for  which  man  may  wish  to  use  it,  and  must  be  ex- 
pended in  producing  some  effect  or  other. 

There  is  still  a  great  deal  of  mystery  about  the  precise 
nature  of  the  changes  which  take  place  in  the  internal  con- 
stitution of  matter,  which  correspond  in  their  effects  to  the 
raising  and  letting  fall  of  weights  in  relation  to  gravita- 
tion. Some  scientific  men  suppose  that  this  up  and  down 
movement,  so  to  speak,  in  chemistry,  is  very  closely  anal- 
ogous in  its  nature  to  that  of  raising  and  letting  fall  a 
weight — that  is  to  say,  that  the  sun,  in  acting  upon  com- 
pound substances  in  plants,  in  some  mysterious  way  sep- 
arates the  elements  to  a  certain  distance  from  each  other, 
and,  still  more  mysteriously,  places  them  in  such  a  condi- 
tion in  relation  to  each  other  that  they  are  kept  apart,  until 


DECOMPOSITION   AND   EECOMPOSITION    OF   WATEK.      195 

finally  they  are  released  from  this  coercion,  and  that  then 
they  come  together  again  with  prodigious  force.  This  fall- 
ing together,  as  these  philosophers  imagine  it,  is  precisely 
analogous  in  its  nature  to  the  coming  together  of  the  earth 
and  the  iron  weight  of  the  pile-driver  when  the  weight  is 
released  from  the  lifters  which  hold  it,  only,  of  course,  the 
distance  through  which  the  force  acts  is  inconceivably 
minute  in  one  case  in  comparison  with  the  other. 

To  show  clearly  what  is  meant  by  this,  we  can  take  the 
case  of  water.  Water  is  composed  of  the  two  substances 
oxygen  and  hydrogen.  In  the  form  of  water  the  two  ele- 
ments are  intimately  united,  and  are  held  together  with 
enormous  force.  There  are  various  ways,  however,  by 
which  this  force  can  be  overcome  and  the  elements  sepa- 
rated. The  separation  may  be  effected  by  the  force  of 
very  great  heat,  or  by  that  of  electricity,  or  by  the  superior 
attraction  for  one  of  the  substances  of  a  third  substance 
brought  into  action  upon  it.  In  some  form  or  other,  how- 
ever, very  great  force  is  necessary  to  separate  these  ele- 
ments from  their  combination  with  each  other  in  water; 
and,  moreover,  after  they  are  once  separated,  they  have  an 
extremely  strong  tendency  to  come  together  again,  and,  in 
coming  together,  to  develop  and  redeliver,  as  it  were,  the 
same  force  that  was  expended  in  separating  them.  Still, 
this  tendency  to  reunite  is  suspended  and  disguised  while 
the  two  elements  remain  coW,just  as  the  tendency  of  the 
pile-driving  weight  to  fall  is  suspended  and  disguised  so 
long  as  it  is  held  by  the  grapple  above. 

A  child  who  should  know  nothing  about  the  construc- 
tion and  action  of  a  pile-driver  might  look  at  one  standing 
on  the  bank  of  a  river,  with  the  weight  raised,  and  have  no 
idea  of  the  force  stored  in  it  and  held  in  suspense  by  the 
brown  mass  of  iron  near  the  top  of  the  guides;  and  when 
this  mass  is  suddenly  released  by  a  slight  movement  of  the 


196  THE   FOUR   CIRCUITS   OF   SOLAR   ENERGY. 

workman  below,  he  is  astonished,  and  perhaps  alarmed,  at 
the  sudden  and  violent  descent  of  it,  and  at  the  tremendous 
force  with  which  it  strikes  upon  the  head  of  the  pile. 

In  the  same  manner,  any  one  might  see  the  two  elements 
of  oxygen  and  hydrogen  brought  into  their  gaseous  form 
in  their  separation  from  each  other,  and,  not  knowing  by 
what  mysterious  means  they  are  held  apart,  would  never 
imagine  what  an  immense  force  is  held  in  suspense  by  the 
condition  in  which  they  are  placed  in  relation  to  each  other; 
and  when,  at  last,  they  are  released  from  this  distention, 
as  they  may  be  by  raising  the  temperature  of  the  smallest 
portion  of  them  up  to  a  certain  point,  we  are  astonished  at 
the  suddenness  and  violence  of  the  force  with  which  they 
rush  into  union  again. 

This  force,  in  all  such  cases,  shows  itself,  in  the  first  in- 
stance, in  the  form  of  heat ;  and  this  is  the  reason  why  it 
is  only  necessary  to  raise  a  minute  portion  of  the  mixture 
to  the  temperature  necessary  for  releasing  them  in  order  to 
release  the  whole ;  for  the  heat  developed  by  the  union  of 
the  first  set  of  particles  affected  raises  the  adjoining  sets 
on  every  side  to  the  right  temperature  for  union,  and  these 
the  next,  and  so  on  with  amazing  rapidity  through  the  en- 
tire mass — the  solar  force  which  had  been  stored  in  them 
by  the  separation  being  brought  again  into  action  by  their 
union  with  such  suddenness  and  rapidity  as  to  produce, 
under  certain  circumstances,  a  violent  explosion. 

In  other  cases,  as  in  the  burning  of  wood,  for  example, 
or  the  reunion  of  the  separated  elements  in  the  bodies  of 
animals,  the  process  is  more  slow.  The  reason  is,  that 
while,  in  the  case  of  two  gases  mingled  together,  the  parti- 
cles of  the  substances  Avhich  tend  to  unite  are  in  close  jux- 
taposition to  each  other,  in  the  case  of  solids,  one  of  the 
substances  is  in  a  compact  mass,  and  the  other  has  no  ac- 
cess to  the  interior  portion  any  faster  than  the  outer  por- 


3LAB  FOECK  KESTOBKD, 


PHILOSOPHY   OP   COMBUSTION.  199 

tions  are  consumed  and  borne  away.  The  chief  substances 
which  are  separated  from  each  other  in  vegetable  growth 
are  carbon  and  hydrogen  from  oxygen,  and  it  is  chiefly  of 
carbon  and  hydrogen,  in  various  forms  and  proportions,  and 
in  various  modes  of  combination,  that  wood  and  nearly  all 
other  vegetable  products  are  composed.  Consequently, 
when  wood  is  set  on  fire,  or,  to  speak  scientifically,  when  a 
portion  of  the  wood  is  raised  to  such  a  temperature  that 
the  carbon  and  hydrogen  can  again  be  seized  by  the  oxy- 
gen of  the  atmosphere,  the  process  of  reunion  can  go  on 
only  so  fast  as  the  outer  layers  of  the  wood  are  wasted 
away,  so  as  to  afford  access  for  the  oxygen  to  the  interior 
portions.  Thus,  though  the  "  falling  together,"  as  it  is  now 
generally  considered,  of  the  oxygen  and  the  carbon,  and 
the  oxygen  and  the  hydrogen,  gives  out  all  the  force,  ei- 
ther as  heat  or  in  some  other  form,  which  was  expended  by 
the  sun  in  separating  them,  the  process  of  reunion,  even  in 
the  greatest  forest  conflagrations,  proceeds  in  a  regular 
and  gradual,  though  sometimes  very  rapid  manner. 

If  there  was  enough  oxygen  at  hand  to  supply  at  once 
all  the  carbon  and  hydrogen  contained  in  the  woods  shown 
to  be  on  fire  in  the  engraving,  the  whole  forest  would  flash 
into  a  flame  in  an  instant  with  an  inconceivably  violent  ex- 
plosion, sufficient  not  only  to  blow  the  horse  and  wagon  to 
atoms,  but  to  shake  the  whole  country  around  with  the 
force  of  the  concussion. 

In  the  case  of  the  animal  organization,  the  liberation  of 
the  force  stored  in  the  food  is  so  regulated,  if  the  organs 
are  in  a  healthy  condition,  as  to  supply  heat  and  mechan- 
ical force  just  so  fast  as  it  is  needed  for  maintaining  the 
life  and  the  movements  of  the  animal ;  for  the  food  which 
the  animal  takes  consists  simply  of  substances  containing 
heat  and  force  from  the  sun,  stored  in  them  by  the  pro- 
cesses of  vegetation,  and  brought  into  such  a  condition 


200  THE    FOUR   CIRCUITS    OF    SOLAK   ENERGY. 

as  to  be  easily  received  and  assimilated  by  the  animal  or- 
gans. 

In  consequence  of  the  form  in  which  the  solar  force  is 
thus  stored,  and  the  wonderful  adaptation  of  the  vital  or- 
gans to  the  work  of  receiving  and  developing  it,  it  is  liber- 
ated within  the  body  of  the  animal  very  gradually,  as  it  is 
needed,  and  often  large  portions  of  it  are  retained  and  are 
not  liberated  at  all,  so  that  when  one  animal  feeds  upon  the 
flesh  of  another,  the  stored  force  is  transferred  in  an  unex- 
pended condition  from  one  organization  to  the  other.  Thus 
the  insect  receives  its  food — that  is,  its  supply  of  stored 
force — from  the  juices  of  the  plants  in  which  a  portion  of 
the  solar  energy  has  been  laid  up  by  the  processes  of  veg- 
etation. The  insect  expends  a  portion  of  this  force  in  his 
creepings,  or  his  leapings,  or  through  his  wings,  but  retains 
a  large  portion  of  it  in  the  tissues  of  his  body  unexpended. 
The  swallow,  in  devouring  many  insects,  transfers  the  en- 
ergy to  his  own  system,  and  expends  large  portions  of  it 
in  giving  the  prodigious  impulse  to  his  wings  necessary  for 
his  rapid  and  tireless  flight ;  he  does  not,  however,  expend 
all  that  he  receives,  but  large  portions  of  it  are  stored  in 
his  flesh,  to  be  transferred  to  the  body  of  the  hawk  or  the 
eagle  when  the  swallow  is  in  his  turn  devoured. 

In  the  same  manner,  the  ox,  in  a  double  sense,  supplies 
force  for  the  use  of  man ;  he  receives  the  solar  energy  that 
is  stored  up  in  the  blades  of  grass  into  his  system;  a  part 
of  this  energy  he  expends  directly  in  drawing  the  loads  or 
plowing  the  fields  of  man,  and  a  part  he  stores  in  his  mus- 
cles and  in  his  flesh,  which  form  the  beef  that  man  uses  for 
food.  In  this  way  the  force  is  transferred  in  an  unexpend- 
ed form  to  the  human  system,  and  man  proceeds  to  expend 
it  in  spading  or  hoeing  the  ground,  or  perhaps  in  guiding 
the  labors  of  the  successor  of  the  ox  that  furnished  him 
with  his  supply.  Thus  it  is  the  solar  force,  in  process  of 


CONTENDING   FORCES.  203 

being  stored,  that  forms  the  grass  of  the  field.  It  is  the 
same  solar  force,  after  it  is  thus  stored  and  has  been  trans- 
ferred to  the  body  of  the  ox,  that  impels  the  plow  ;  and  it 
is  the  same — that  is,  a  portion  of  the  same,  after  a  double 
transfer — that  is  exercised  by  the  higher  organs  of  man  in 
superintending  and  directing  the  whole  operation. 

Thus,  in  its  circuit  through  the  organs  of  vegetable  and 
animal  life,  the  solar  force  is  brought  by  slow  degrees  into 
action  in  the  animal  system,  in  proportion  as  it  is  required, 
for  the  various  purposes  of  life.  It  may  be  brought  into 
action  also  in  the  same  gradual  manner  without  passing 
into  any  animal  organization,  for  the  carbon  and  hydrogen 
may  be  made  to  recombine  with  oxygen,  and  thus  deliver 
out  the  force  which  the  sun  exercised  in  separating  them 
in  a  great  many  other  ways. 

The  currents  of  solar  energy,  in  the  different  circuits 
which  they  pursue,  may  and  often  do  come  into  opposition 
and  conflict  the  one  against  the  other.  We  have  innumer- 
able examples  of  this  in  the  ordinary  phenomena  of  nature 
as  witnessed  around  us.  A  very  familiar  example  of  it  is 
afforded  in  the  spectacle  of  a  steamer  ascending  a  river 
against  the  current  by  the  force  derived  from  the  combus- 
tion, under  the  boiler,  of  wood  taken  from  the  bank  of  the 
stream,  as  is  shown  in  the  engraving,  and  is  seen  every  day 
on  the  Mississippi  River. 

The  flow  of  the  stream  is  produced,  as  was  shown  in  the 
preceding  chapter,  by  the  falling  force  of  water  raised  into 
the  air  by  the  solar  radiation — that  is,  by  that  portion  of 
the  solar  energy  that  performs  its  circuit  through  the  wa- 
ter and  the  air.  The  force  by  which  the  engine  of  the 
steamer  is  driven  is  derived  from  the  wood  which  grew 
upon  the  bank ;  for  the  steam  is  in  no  sense,  as  is  often  sup- 
posed, the  source  of  the  impelling  power,  but  only  the  vehi- 
cle of  it.  In  other  words,  the  force  which  carries  the  steam- 


204  THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

er  against  the  current  is  the  force  set  free  by  the  combustion 
of  the  wood — that  is,  by  the  reunion,  with  great  eagerness, 
of  elements  separated  from  each  other  by  the  same  amount 
of  solar  energy  acting  through  the  organs  of  vegetable  life. 
The  two  forces  shown  in  action  in  the  engraving,  one  act- 
ing upon  the  water,  and  through  it  upon  the  bottom  of  the 
vessel,  and  tending  to  carry  the  vessel  down  the  stream, 
and  the  other  that  of  the  revolving  paddles  driven  by  the 
action  of  the  heat  through  the  intervention  of  the  steam, 
meet  and  oppose  each  other,  and  the  strongest  carries  the 
day. 

In  this  case  the  contest  is  quite  a  gentle  one,  and  the  vic- 
tory is  gained  with  very  little  manifestation  of  violence  on 
either  side ;  but  in  other  cases  the  struggle  is  often  a  fear- 
ful one,  and  the  victory  for  a  long  time  doubtful.  The 
next  engraving  represents  the  struggle  between  the  force 
evolved  from  coal  and  that  of  the  sun  acting  through  the 
air  and  water  in  the  winds  and  waves,  which  is  often  ex- 
emplified in  the  passage  of  a  French  or  English  steamer  in 
crossing  the  Atlantic. 

The  scientific  student  must  cease  to  regard  the  steam  in 
these  cases  as  in  any  sense  the  source  of  the  power.  It  is 
only  the  vehicle  by  which  the  force  is  conveyed ;  for  the 
true  source,  as  has  already  been  said,  is  the  coal.  It  is 
common  to  speak  in  popular  language  of  the  power  of 
steam,  but  the  power  of  steam  is  only  a  power  of  the  kind 
that  is  exerted  by  one  end  of  a  pole  when  a  man  is  push- 
ing at  the  other  end — that  is,  it  is  in  all  cases  power  im- 
parted to  it,  and  transmitted  through  it.  When  the  fires 
go  out  under  the  boiler,  the  ppwer  of  the  steam  comes  to 
ah  end.  All  its  boasted  energy  ceases  at  once,  and  it  be- 
comes as  inert,  and  as  helpless,  and  as  incapable  of  carry- 
ing on  any  work  by  itself  as  the  cranks,  or  piston-rods,  or 
any  other  lifeless  part  of  the  machinery. 


FORCE   IMPRISONED   IN   COAL.  207 

Nor  is  the  coal  itself  any  more  an  original  source  of  the 
power  by  which  the  machinery  is  worked.  It  is  the  source 
only  in  the  sense  of  being  the  substance  in  which  the  force 
is  stored,  ready  to  be  called  into  action  by  the  will  of  man. 
The  real  source,  and  the  original  one,  so  far  as  we  can  at 
present  trace  it,  is  the  sun. 

That  is  to  say,  as  was  explained  in  the  last  chapter,  the 
sun,  by  its  action  upon  the  organs  of  vegetation  in  the 
leaves  of  plants,  separates  the  carbon  and  hydrogen  from 
their  natural  combinations,  and  fixes  them  mysteriously  in 
some  new  combinations,  without,  however,  at  all  diminish- 
ing the  great  strength  of  their  tendency  to  come  together 
again ;  but,  for  some  reason  not  understood,  this  tendency 
can  only  come  into  action  very  slowly  under  ordinary  tem- 
peratures, though  it  bursts  into  great  intensity  of  action 
when  the  temperature  is  raised  above  a  certain  point,  pro- 
vided the  oxygen  with  which  the  carbon  and  hydrogen 
wish  to  unite  is  at  hand.  If,  however,  the  carbon  and  hy- 
drogen are  kept  beyond  the  reach  of  oxygen,  they  have, 
of  course,  no  opportunity  to  reunite,  and  the  store  of  re- 
served force  will  remain  unexpended  for  an  indefinite  pe- 
riod. 

This  happens  when  the  wood,  or  any  other  vegetable 
product,  is  kept  under  water,  for  then  there  is  no  oxy- 
gen accessible  to  combine  with  the  imprisoned  elements. 
It  is  true  that  the  water  itself  contains  a  large  supply  of 
oxygen,  but  it  is  oxygen  which  is  not  free.  It  is  already 
combined  with  its  full  proportion  of  hydrogen,  and  can  take 
no  more.  Wood,  therefore,  that  is  kept  immersed  under 
water  will  retain  its  reserved  force  for  an  indefinite  period. 

Now  it  happens  that  there  are  various  ways  by  which 
large  quantities  of  wood  and  other  products  of  vegetation 
are  accumulated  in  vast  masses,  which  are  submerged  in 
water  and  preserved,  and  in  the  end  become  beds  of  coal. 


208  THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

These  beds  of  coal,  of  course,  contain  enormous  stores  of 
solar  energy,  which  were  deposited  in  the  substance  of  them 
years  ago,  when  they  were  formed.  The  traces  of  the  an- 
cient vegetable  origin  of  the  beds  are  found  very  abundant- 
ly in  the  structure  of  the  coal  when  examined  by  the  mi- 
croscope and  by  other  means. 

There  are  various  natural  processes  by  which  such  de- 
posits of  vegetable  matter  are  now  being  formed. 

One  is  by  the  "  rafts,"  so  called,  formed  by  the  floating 
trees  which  accumulate  at  or  near  the  mouths  of  certain 
great  rivers  flowing  through  countries  covered  with  for- 
ests. Immense  quantities  of  this  stored  force  are  carried 
down  every  year  by  the  Mississippi,  and  by  the  great  riv- 
ers of  Asia,  until  they  reach  the  mouths  of  them,  or  the 
flat  land  near  the  mouths,  where  they  become  matted  to- 
gether in  vast  masses  which  float  upon  the  surface  of  the 
water,  or,  being  sunk  by  the  weight  of  the  roots  and  of  the 
earth  adhering  to  them,  become  water-logged,  and  form  the 
foundation  of  shoals,  or  even,  in  process  of  time,  of  islands. 

In  other  cases  aquatic  plants  have  grown  up  from  the 
bottoms  of  shallow  lakes,  spreading  their  leaves  over  the 
surface  of  the  water  until  the  mud  at  the  bottom  is  so  filled 
in  every  part  by  the  ramifications  of  the  roots,  that,  in  the 
end,  the  whole  stratum  in  which  they  grow  is  made  buoy- 
ant with  them,  and  it  rises  to  the  surface,  and  covers  the 
water  with  a  floating  field,  as  it  were,  on  which,  in  time, 
mosses  and  lichens,  and  at  last  shrubs  and  bushes  grow. 
The  lake  is  thus  transformed  into  a  bog,  the  soil  and  the 
vegetation  growing  upon  it  being  supported,  in  a  some- 
what unstable  and  fluctuating  condition,  by  the  water  be- 
low. As  the  thickness  of  this  layer  increases  by  earthy 
matter  brought  upon  it  by  the  wind,  and  by  the  decay  of 
the  vegetation  which  gathers  upon  it,  the  whole  mass  grad- 
ually subsides,  until  at  length,  in  the  course  of  ages,  the 


FORMATION    OF   COAL   DEPOSITS.  209 

•whole  basin  of  the  lake  may  be  filled  with  vegetable  mat- 
ter submerged  in  water  and  so  preserved,  thus  holding 
the  enormous  store  of  solar  force  of  which  it  is  the  custo- 
dian for  the  use  perhaps  of  man  in  future,  and  often  very 
distant  ages. 

There  is  another  mode  still  in  which  vast  accumulations 
of  vegetable  matter  are  at  the  present  day  in  the  process 
of  formation  on  the  earth's  surface,  and  that  is  by  the  slow 
growth  and  accumulation  of  peat  in  bogs.  If  this  forma- 
tion takes  place  in  a  tract  which  is  slowly  subsiding,  the 
peat  may  form  to  a  great  thickness  in  the  course  of  ages, 
and  the  vegetable  material  so  accumulating  may  be  pre- 
served by  the  constant  infiltration  of  water  as  the  ground 
subsides,  or  even  without  subsidence  by  an  increase  of  the 
deposit  over  an  extensive  area. 

In  all  these  cases  the  tract  in  which  these  vegetable  de- 
posits are  formed  may  subsequently  subside,  and  be  cov- 
ered by  strata  of  sand  or  gravel  washed  over  them.  If  the 
subsidence  goes  on,  new  depressions  may  be  formed  and 
new  deposits  of  vegetable  matter  produced  above  the  oth- 
ers, and  be  separated  from  them  by  strata  of  sand,  or  grav- 
el, or  clay  hardened  into  strata  of  rock.  Processes  pre- 
cisely analogous  to  these  are  now  slowly  going  on  in  va- 
rious parts  of  the  earth,  and  there  is  abundant  reason  for 
believing  that  in  former  ages  they  went  on  on  a  vastly 
more  extended  scale  than  we  witness  at  present,  and  the 
immense  beds  of  coal  alternating  with  strata  of  slate  and 
sandstone  formations  which  now  constitute  the  "coal-meas- 
ures," so  called,  of  England  and  America,  as  well  as  of  vari- 
ous other  portions  of  the  earth,  may  have  thus  been  formed. 

The  quantity  of  reserved  force  thus  stored  among  the 
strata  beneath  the  surface  of  the  ground,  and  the  extent 
to  which  they  are  annually  drawn  upon  for  the  purposes 
of  man,  are  enormous. 


210  THE    FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

Great  Britain,  it  is  estimated,  brings  out  of  the  earth 
from  her  mines  about  20,000,000  tuns  of  coal  annually,  and 
the  stored  force  which  she  thus  brings  into  action  is  equal 
to  that  which  would  be  realized  from  the  labor  of  about 
133,000,000  of  men,  which  is  probably  ten  or  twenty  times, 
and  perhaps  fifty  times  the  force  of  all  the  laboring  men  in 
the  kingdom.  This  is  one  secret  of  the  immense  power  to 
which  England  has  attained.  With  only  perhaps  five  mil- 
lion of  laborers  to  feed  and  clothe,  she  enables  these  labor- 
ers, by  means  of  the  stored  solar  force  in  the  coal,  to  do  • 
the  work  of  more  than  a  hundred  and  thirty  millions.  By 
means  of  the  human  energy  thus  re-enforced,  she  manufac- 
tures iron,  and  lays  down  railroads,  and  builds  ships,  and 
spins  and  weaves  for  half  the  world. 

The  question  of  the  amount  of  coal  accessible  to  man 
contained  in  the  geological  formations  of  any  country  de- 
pends not  only  upon  the  extent  laterally  of  the  coal-bear- 
ing strata,  but  upon  the  depth  to  which  they  can  be  worked. 
And,  singularly  enough,  the  question  of  depth  does  not  de- 
pend upon  the  difficulty  of  raising  the  weight  through  so 
great  a  distance,  inasmuch  as  the  coal  itself;  or,  rather,  the 
force  that  is  stored  in  it,  does  that — that  is  to  say,  the  force 
developed  by  the  combustion  of  a  part  of  the  coal  serves 
to  raise  the  other  part,  with  all  its  store  of  force  retained 
in  it,  up  to  the  surface,  whatever  the  depth  may  be.  The 
real  difficulty  which  puts  a  limit  to  the  possible  depth  of 
these  excavations  is  the  heat ;  for  the  heat  is  found  to  in- 
crease regularly,  and  so  rapidly  that  at  the  depth  of  four 
thousand  feet  the  temperature  of  the  mine,  through  that 
of  the  rocks  which  it  traverses  at  that  depth,  becomes  about 
105°,  and  it  is  not  possible  for  laborers  to  continue  to  work 
with  the  surrounding  air  at  a  higher  temperature  than 
that,  even  with  all  the  relief  which  can  be  obtained  by  the 
best  known  means  of  ventilation. 


VAST   STOKES   OF   FORCE.  211 

So  that  the  question  for  any  country,  in  respect  to  its 
store  of  reserved  force,  is  to  determine  how  long  the  sup- 
ply of  coal  will  last  that  is  contained  in  all  the  strata  un- 
derneath it  down  to  the  depth  of  four  thousand  feet. 

Many  different  calculations  have  been  made  within  a  few 
years  past  to  determine  how  long  the  supply  of  coal  buried 
in  the  bowels  of  the  earth  in  England  will  last,  and  the 
results  vary  enormously — from  a  few  hundred  to  many 
thousand  years.  A  commission  of  scientific  men  recently 
appointed  to  examine  this  question  came  to  the  conclusion 
that  at  the  present  rate  of  consumption  the  supply  would 
last  about  thirteen  hundred  years;  but  with  a  consump- 
tion increasing  in  the  future  at  the  rate  at  which  it  has 
been  increasing  for  a  few  years  past,  the  supply  would  be 
exhausted  in  about  two  hundred  and  eighty  years.  Other 
estimates  have  been  made,  however,  which  give  much  lon- 
ger periods  than  these. 

The  stores  of  coal  held  in  reserve  by  the  strata  that  un- 
derlie the  continent  of  America  are  vastly  greater  even 
than  those  of  England  ;  they  are,  indeed,  practically  incal- 
culable. It  is  only  a  very  small  beginning  that  has  yet 
been  made  in  bringing  into  use  the  immense  supplies  of 
stored  force  thus  held  in  reserve  for  the  present  and  future 
generations. 

There  is  something  very  interesting  and  curious  in  the 
principles  which  govern  the  redevelopment  of  the  force 
held  in  reserve  by  combustible  substances ;  for  a  combus- 
tible substance  is,  in  principle,  one  the  particles  of  which 
have  been  separated  by  the  sun  from  those  of  some  other 
substance  toward  which  they  have  an  immensely  powerful 
tendency  of  attraction.  This  tendency,  inconceivably  great 
as  it  is,  takes  effect  through  distances  so  minute  that  we 
can  not  directly  perceive  the  action  of  it;  we  can  only  ob- 


212  THE   FOUR  CIRCUITS   OF   SOLAK   ENERGY. 

serve  its  effects ;  and  combustion  is  simply  the  reunion  of 
these  separated  elements  under  favorable  conditions  by 
which  the  force  with  which  they  combine  is  fully  devel- 
oped, and  manifests  itself  in  the  evolution  of  intense  light 
and  heat. 

If  the  substance  is  a  gas,  the  light  and  heat  developed 
take  the  form  of 'flame  ;  if  a  solid,  the  light  and  heat  liber- 
ated give  it  the  form  of  burning  coals. 

The  chief  substances  which  are  thus  separated  from  each 
other,  to  combine  again  afterward  with  the  evolution  of 
light  and  heat,  are  hydrogen  and  carbon  on  the  one  hand, 
and  oxygen  on  the  other.  It  is  found  by  careful  experi- 
ments that  the  amount  of  heat,  or,  rather,  of  force  in  the 
form  of  heat  which  is  developed  by  the  combustion — that 
is,  by  the  reunion  of  the  oxygen  with  the  hydrogen  and 
carbon — is  generally  in  proportion  to  the  amount  of  oxy- 
gen so  recombined;  and  consequently,  as  the  elements  above 
named,  and  others  not  so  common,  as  in  that  of  sulphur, 
for  example,  demand  different  quantities  of  oxygen  to  sat- 
isfy their  different  appetites,  the  heat  furnished  by  the  com- 
bustion of  them  is  very  different  in  the  different  cases,  the 
combustion  of  hydrogen  giving  the  greatest  heat,  that  of 
carbon  coming  next,  and  that  of  sulphur  least. 

Thus  the  force  stored  in  different  kinds  of  fuel  varies  in 
a  considerable  degree  with  the  different  proportions  in 
which  they  contain  the  above  elementary  substances  in 
their  composition,  and  the  quantity  of  heat — that  is,  of 
force  in  the  form  of  heat — has  been  carefully  ascertained. 
Some  of  the  principal  amounts  are  given  in  the  following 
table.  In  order  fully  to  appreciate  the  values  expressed  in 
the  last  column,  the  reader  must  remember  that  a  unit  of 
heat  is  the  quantity  required  to  raise  a  pound  of  water 
from  its  condition  when  just  melted  from  ice  one  degree  of 
Fahrenheit's  thermometer.  To  raise  it,  consequently,  from 


FOKCE  DEVELOPED  BY  COMBUSTION.         213 

the  freezing  to  the  boiling  point — that  is,  from  32°  to  212°, 
would  require  about  180  units  of  heat  for  each  pound.* 

And  each  of  such'units  of  heat  is  equivalent,  as  has  al- 
ready been  shown,  to  772  foot-pounds — that  is,  it  repre- 
sents a  force  sufficient  to  raise  a  pound  weight  772  feet  into 
the  air,  or  that  which  would  be  developed  by  the  fall  of  a 
pound  weight  through  that  distance. 

The  following  table,  then,  shows  the  number  of  units  of 
heat  developed  by  the  combustion  of  the  several  substances 
named  in  it.  The  letters  in  the  second  column  denote  the 
words  carbon,  hydrogen,  and  sulphur: 

TAHLE.f 

Substance.  Composed  of.  Units  of  Heat. 

Hydrogen 11.             f)C,000 

Petroleum C.  and  H 22,000 

Spermaceti C.  and  II 18,000 

Charcoal C.             14,500 

Anthracite  Coal C.             14,000 

Sulphur S.              3,500 

These  figures  denote,  of  course,  the  total  amount  offeree 
which  is  stored  in  these  several  substances,  or,  rather,  in 
their  condition  in  relation  to  the  oxygen  which  surrounds 
them,  and  which  is  actually  brought  into  action  when  the 

*  Not  exactly,  however,  since  it  is  found  that  the  quantity  required  to 
produce  an  increase  of  one  degree  in  the  temperature  varies  slightly  as  the 
temperature  increases.  The  amount  also  is  very  different  for  different 
substances ;  that,  however,  which  is  required  for  water  at  a  temperature 
of  32°  is  made  the  standard  of  measurement. 

t  In  such  tables  as  these,  the  numbers  given  can,  of  course,  only  be  con- 
sidered as  approximations  to  the  truth,  since,  in  ascertaining  values  so  ex- 
tremely difficult  of  precise  determination,  different  experimenters  will,  of 
course,  reach  somewhat  different  results.  The  young  student  in  science 
will  also  find  in  different  books  tables  differing  at  the  first  view  very  de- 
cidedly from  each  other,  owing  to  the  fact  that  some  use  the  degrees  of 
Fahrenheit's  thermometer,  and  others  those  of  the  Centigrade  in  desig- 
nating units  of  heat. 


214  THE   FOUR   CIRCUITS    OP   SOLAR   ENERGY. 

oxygen  reunites  with  them.  It  is  only  a  small  part  of  this 
total  amount  that  can  be  really  utilized — that  is,  made  to 
serve  a  useful  purpose  by  any  of  the  contrivances  of  man. 
It  is  calculated  that  only  from  one  twentieth  to  one  tenth 
of  the  amount  offeree  stored  in  coal  can  be  made  effective 
for  useful  work  in  the  best  constructed  steam-engines  that 
have  hitherto  been  employed,  though  a  London  firm,  it  is 
said,  have  recently  made  improvements  by  which  they 
claim  that  one  fifth  of  the  whole  amount  can  be  utilized. 
Even  at  this  rate  far  the  largest  portion  is  wasted,  and  a 
wide  field  is  open  for  future  engineers  and  inventors  in 
devising  arrangements  for  greatly  increasing  the  benefit 
which  generations  to  come  may  derive  from  the  store  of 
energy  which  nature  has  laid  up  in  the  beds  of  peat  and 
coal  for  their  use. 

Still,  notwithstanding  the  imperfection  of  the  appliances 
by  means  of  which  this  stored  force  is  used,  the  saving  of 
human  strength  by  the  employment  of  it  is  immense.  The 
stones  used  in  the  construction  of  the  great  pyramid  of 
Egypt  have  been  calculated  to  weigh,  in  all,  about  12,000 
millions  of  tons,  and  it  required  the  labor,  it  is  said,  of 
100,000  men  for  twenty  years  to  raise  them  and  put  them 
in  place.  Dr.  Lardner  calculated  that  the  force  developed 
by  the  combustion  of  480  tons  of  coal  would  have  been  suf- 
ficient to  do  the  same  work. 

And  yet  Great  Britain  employs  for  her  various  purposes 
the  force  contained  in  20  millions  of  tons  every  year. 

It  will  assist  the  student  to  fix  the  principles  above  ex- 
plained in  his  mind,  and  to  enlarge  his  conception  of  the 
extent  to  which  all  the  manifestations  of  physical  energy 
which  he  sees  around  him  are  effects  derived  ultimately 
from  the  radiation  of  the  sun,  if  he  should  analyze  some  of 
these  phenomena  as  he  observes  them,  and  trace  back  the 


THE   BfN   OITINQ   1IELP. 


VARIOUS   RESULTS.  217 

chain  of  causes  that  produce  them  to  their  origin  in  the 
sun.  The  results  he  will  find  in  some  cases  quite  curious. 

Take,  for  example,  the  case  of  the  light-house  upon  a  rock 
at  sea.  The  light  in  the  lantern  conies  from  the  combus- 
tion of  oil,  this  combustion  consisting  simply  in  the  libera- 
tion, in  the  form  of  light  and  heat,  of  the  force  stored  in 
the  oil.  This  oil  was  elaborated  in  the  body  of  the  whale 
from  substances  containing  stores  offeree  which  served 
the  whale  as  food ;  and  these,  if  traced  back  to  their  origin, 
came  from  the  agency  of  the  sun  in  separating  the  carbon 
and  the  hydrogen  from  the  oxygen  in  some  vegetable  or- 
ganization, or  some  organization  on  the  confines  of  the 
vegetable  and  animal  world,  which  fulfilled  the  ordinary 
functions  of  vegetation.  In  this  forcible  separation  of  these 
elements,  a  portion  of  the  solar  energy  was  absorbed  and 
stored.  Thus  the  light  that  beams  from  the  lantern  of  the 
light-house  is  a  light  which  may  be  traced  back  by  a  cir- 
cuitous route,  and  through  various  forms  and  disguises,  to 
the  sun. 

In  the  same  manner,  though  by  a  very  different  path, 
the  force  by  which  the  winds  and  the  waves  are  impelled 
comes,  as  we  have  already  seen,  from  the  agency  of  the 
solar  beams.  Thus  the  solar  force,  coming  by  one  path  and 
reappearing  in  one  form,  sends  help  to  the  mariner  to  aid 
him  in  making  his  way  through  the  perils  with  wrhich  the 
same  force  in  another  form  environs  him.  In  other  words, 
the  force  which  the  sun  stores  in  the  oil  is  used  to  guard 
against  the  mischief  which  might  flow  from  that  which  he 
stores  in  the  water  and  in  the  air. 

And  even  in  cases  where  the  force  which  comes  through 
one  circuit  can  not  be  made  actually  to  help,  it  may  be  em- 
ployed to  give  warning. 

This  is  shown  in  the  engraving  of  what  is  called  a  bell- 
buoy,  which  consists  of  a  floating  structure  bearing  a  low 
K 


218  THE   FOUE   CIRCUITS   OF   SOLAE   ENEBGY. 

open  tower  or  cage,  within  which  is  suspended  a  bell,  which 
is  rocked  and  swung  incessantly  by  the  motion  of  the  sea, 
without  the  aid  of  any  human  attendant.  These  buoys  are 
mainly  useful  in  fogs,  whether  occurring  by  day  or  night, 
in  either  of  which  cases  a  light-house  would  be  useless. 
Now  the  fog,  as  we  have  already  seen,  is  produced  by  solar 
agencies  acting  through  the  water  and  air,  and  the  motion 
of  the  waves,  and  the  consequent  rocking  of  the  buoy  and 
ringing  of  the  bell,  are  the  results  of  the  same  energy  act- 
ing in  a  different  portion  of  the  same  great  circuit.  In  this 
case,  accordingly,  the  sun,  in  one  division  of  the  same  cir- 
cuit, applies  his  energy  in  giving  warning  and  information 
to  man  to  save  him  from  dangers  which  he  creates  by  his 
action  in  another  division. 

Only  one  of  the  most  simple  of  the  forms  in  which  the 
solar  energy  takes  effect  in  the  processes  of  vegetation, 
namely,  the  separation  of  carbon  and  hydrogen  from  oxy- 
gen, has  been  particularly  dwelt  upon  in  this  chapter,  inas- 
much as  it  is  only  the  general  principle  of  the  storage  of 
that  energy  in  vegetable  tissues  which  was  to  be  here  illus- 
trated. The  real  processes,  as  they  take  place  in  nature, 
are  infinitely  complicated.  It  is  not  even  known  in  pre- 
cisely what  way,  nor  in  what  proportions,  the  different  kinds 
of  solar  radiation  act  in  the  processes  of  vegetation,  though 
there  is  good  reason  to  believe  that  the  third  of  the  three 
classes,  namely,  the  actinic  rays,  act  a  very  important,  if 
not  the  most  important  part.  The  substances,  moreover, 
both  simple  and  compound,  with  which  the  sun  has  to 
deal,  are  infinite  in  number,  and  his  modes  of  dealing  with 
them  in  the  different  organizations  of  vegetable  and  animal 
life  are  infinitely  varied.  The  forces  brought  into  action, 
the.  separations,  the  changes,  the  combinations  and  recom- 
binations which  are  produced,  are  absolutely  without  end. 
Though  great  numbers  of  scientific  men  have  for  the  last 


RECAPITULATION.  221 

quarter  of  a  century  been  devoting  their  lives  to  the  work 
of  exploring  this  field,  they  all  feel  that  the  work  is  but 
just  begun.  The  farther  they  advance,  the  more  numerous 
are  the  vistas  which  open  before  them  of  regions  of  wonder 
and  mystery  into  which  they  are  not  yet  able  to  make 
their  way. 

The  general  principle,  however,  as  explained  in  this  chap- 
ter, is  well  established,  and  it  is  one  that  every  well-in- 
formed man  should  understand,  namely,  that  the  world  of 
vegetable  and  animal  life  is,  in  respect  to  the  physical  phe- 
nomena which  it  manifests,  a  system  for  gathering,  and 
storing,  and  afterward  transmitting  and  expending  in  va- 
rious ways  the  energy  derived  from  the  sun.  This  energy 
is  mainly  received  and  stored  by  the  action  of  vegetation, 
and  is  held  in  reserve  in  the  tissues  of  plants.  Through 
these  tissues  portions  of  it  are  transferred  in  the  form  of 
food  to  the  organizations  of  animals,  where  it  furnishes  a 
supply  offeree  for  the  vital  functions  of  the  animal  system, 
and  for  the  locomotive  organs  which  animals  require  to 
have  constantly  in  readiness  for  action.  Other  portions 
of  this  force  remain  in  the  tissues  of  the  plants,  whence 
they  gradually  pass  off  into  the  surrounding  air  as  the 
plants  slowly  decay,  or  are  preserved  through  countless 
ages  in  the  substance  of  peat,  or  coal,  or  petroleum,  to  be 
ultimately  brought  into  action  for  the  purposes  of  man. 

And  what  is  very  wonderful,  if  true,  is,  that  even  the  or- 
gans of  the  brain,  through  which,  in  some  mysterious  way, 
the  mind  performs  its  functions,  are,  as  is  now  supposed, 
dependent  on  supplies  of  this  reserved  force  for  their  vig- 
orous and  healthy  action.  In  other  words,  not  only  the 
senses  of  seeing,  hearing,  and  the  like,  but  the  more  purely 
mental  operations  of  thought,  of  reasoning,  of  imagination, 
and  of  memory  are  performed  in  some  mysterious  way 
through  the  agency  of  organs  which,  in  their  healthful 


222  THE   FOUR   CIRCUITS    OF   SOLAR   ENERGY. 

working,  expend  large  portions  of  this  force  which  has 
been  received  into  the  system  with  the  food.  This  is  won- 
derful, and  it  is  a  truth,  if  it  is  a  truth,  which  is  received 
at  present  with  much  caution  by  scientific  men;  but  the 
evidence  which  is  constantly  coming  into  view  strongly 
tends  to  establish  it. 

Thus  the  force  of  the  solar  radiation,  in  entering  into  our 
atmosphere  and  acting  upon  the  surface  of  the  earth,  di- 
vides itself  into  a  thousand  streams,  and  sets  in  motion  a 
countless  number  of  different  agencies.  It  blows  in  the 
wind ;  it  falls  in  the  rain  ;  it  rolls  in  the  waves  of  the  sea ; 
it  undermines  and  disintegrates  the  rocks  along  every 
shore ;  it  constitutes — or,  at  least,  sustains — the  strength 
of  the  lion,  the  fierceness  of  the  tiger,  the  patient  toil  of  the 
ox,  and  even  the  sagacity  of  the  elephant  and  the  cunning 
of  the  fox ;  and  in  the  mysterious  mechanism  of  the  or- 
gans through  which  alone  the  human  mind  can  act,  in  the 
present  state  of  its  existence,  it  expends  itself  in  producing 
the  incessant  and  joyous  activity  of  youth,  and  perhaps  in 
sustaining  the  thoughtful  reasonings  and  the  far-reaching 
memories  of  age.  It  is  thus  the  source  and  sustainer  of 
almost  every  kind  of  action  which  we  see  taking  place 
around  us  on  the  earth.  In  the  dawn  of  human  civiliza- 
tion, if  the  philosophers  of  those  days  had  any  glimpses  of 
these  truths,  it  would  not,  therefore,  seem  at  all  surprising 
that  they  established  ceremonies  of  the  nature  of  worship 
in  honor  of  the  Sun. 


MISS  RANDOM'S  COUSIN.  223 


CHAPTER  XIH. 

SCIENCE    AND    SENTIMENT. 

THOSE  who  have  read  the  volume  of  this  series  entitled 
Water  and  Land  will  perhaps  recollect  that  Lawrence  had 
an  acquaintance  and  friend  named  Theodora  Random,  a 
young  lady  of  about  sixteen  years  of  age,  who  was  gen- 
erally away  at  school  at  New  York,  though  she  spent  her 
vacations  at  home  in  the  town  of  Carlton,  where  Lawrence 
was  now  residing. 

Now  this  Miss  Random  had  a  cousin  named  Roundell, 
who  was  at  this  time  a  law  student.  Lawrence  and  Roun- 
dell were  classmates  in  college,  but  after  they  left  college 
their  paths  seemed  to  diverge,  for  Roundell  commenced 
the  study  of  the  law,  while  Lawrence  had  chosen  engineer- 
ing in  some  of  its  branches  as  his  pursuit  in  life,  and  had 
gone  to  a  scientific  institute  to  study  mathematics  and 
physics. 

About  the  time  that  the  incidents  related  in  this  volume 
were  occurring,  Roundell  came  to  make  a  visit  at  Carlton, 
and  he  and  Lawrence  renewed  their  acquaintance  with  each 
other,  and  they  took  many  walks,  and  held  many  conversa- 
tions together  in  regard  to  their  plans  of  life,  and  the  pro- 
fessions to  which  they  had  respectively  devoted  themselves. 

One  pleasant  morning,  Dorrie,  as  Theodora  was  often 
called,  conceived  the  idea  of  taking  her  pencils  and  paper, 
and  her  little  sister  Jenny,  and  going  out  into  the  woods 
to  a  place  called  the  Cascade,  on  what  she  called  a  drawing 
excursion.  Her  plan  was  to  find  some  pretty  little  object, 


224  SCIENCE    AND   SENTIMENT. 

or  group  of  objects,  that  would  form  the  subject  of  a  design 
for  her  sketch-book. 

Mr.  Roundell,  as  it  happened,  came  to  the  house  to  call 
upon  his  cousin  just  as  she  was  setting  out  upon  her  ex- 
cursion, and  when  he  learned  where  she  was  going,  he  said 
that  he  would  accompany  her. 

"  Very  good,"  said  Dorrie ;  "  only  I  am  not  going  to  have 
you  look  over  me  while  I  am  drawing." 

"  And  I  will  go  and  get  Lawrence  to  go  too,"  said  Mr. 
Roundell,  without  noticing  Dome's  prohibition  in  respect 
to  looking  over  her.  "He  likes  such  excursions." 

"  If  you  do  that,"  said  Dorrie,  "  you  will  do  it  on  your 
own  responsibility.  You  must  consider  it  as  against  my 
express  orders." 

Mr.lloundell  saw  at  once,  by  a  certain  sly  and  significant 
look  upon  Dome's  face,  that  she  was  not  in  earnest  in  this ; 
so  he  proposed  that  she  should  go  on  till  she  reached  a 
certain  place  which  he  designated,  and  wait  there  until  he 
and  Lawrence  came  and  joined  her. 

"  Well,"  said  Dorrie, "  if  you  will  go,  you  must,  I  suppose ; 
but  I  hope  you  won't  find  him  at  home." 

Mr.  Roundell  paid  no  attention  to  this,  but  went  in  search 
of  Lawrence,  while  Dorrie,  with  a  small  portfolio  under  her 
arm,  and  her  pencils  in  their  case  in  her  pocket,  set  off  with 
her  little  sister  to  walk  by  another  Avay  toward  the  ap- 
pointed place  of  meeting. 

This  place  of  meeting  was  a  very  pretty  spot  near  a 
stream,  where  Lawrence  had  made  a  seat  some  time  before, 
which  seat  had  become  a  favorite  resting-place  for  all  the 
young  persons  of  the  village  when  walking  in  that  direc- 
tion. The  seat  was  formed  in  a  somewhat  curious  way. 
Lawrence  had  observed  two  young  trees  growing  pretty 
near  together,  upon  a  smooth  grass-plot  in  a  place  shelter- 
ed by  quite  a  little  grove  growing  behind  it,  and  had  con- 


LAWRENCE'S  SEAT.  225 

ceived  the  idea  of  using  those  trees  as  a  support  for  the 
back  of  a  seat.  So  he  bent  the  trees  into  the  right  inclina- 
tion for  such  a  purpose,  and  confined  them  in  that  position 
till  they  had  become  fixed  in  it.  Then  he  put  two  short 
posts  in  the  ground,  one  in  front  of  each  tree,  and  at  the 
proper  distance  to  form  the  breadth  of  the  seat.  He  nailed 
cleats  across  from  the  top  of  these  supports  to  the  lower 
part  of  the  trees,  arranging  the  whole  so  that  the  plank 
which  was  to  serve  for  the  seat,  when  placed  upon  the 
cleats,  should  be  at  the  right  distance  above  the  ground. 
He  then  procured  a  piece  of  plank  long  enough  to  afford 
room  for  two  or  three  persons  to  sit  upon  it,  and,  after 
smoothing  it  and  rounding  the  edges,  he  fastened  it  to  the 
cleats.  He  also  nailed  a  narrow  board  against  the  trees 
at  the  proper  height  to  form  a  support  to  the  back  for  per- 
sons not  quite  full  grown. 

Thus  he  formed  a  very  comfortable  and  quite  a  durable 
seat ;  and  as  it  was  in  a  very  pleasant  spot,  pretty  open, 
though  sheltered  by  a  grove  in  the  background,  and  not 
far  from  the  stream  at  a  spot  where  the  water  fell  over 
the  rocks  in  the  bed  of  it  in  quite  a  picturesque  manner,  it 
is  not  at  all  surprising  that  "  Lawrence  Wollaston's  seat," 
as  it  was  called,  soon  became  a  favorite  resting-place  for 
young  people  making  excursions  in  that  region. 

The  trees,  moreover,  notwithstanding  the  nails  driven 
into  the  stem  of  them,  continued  to  grow,  and,  as  Law- 
rence watched  the  growth  of  the  new  shoots  from  the  top 
from  time  to  time,  and  trimmed  them  a  little  as  occasion 
required,  he  gradually  aided  the  trees  to  form  a  sort  of 
canopy  of  foliage  over  the  seat,  which  greatly  added  to  the 
attractiveness  of  the  place,  especially  in  warm  and  sunny 
days. 

It  was  at  this  place,  as  has  already  been  said,  that  Miss 
Random  and  her  sister  were  to  wait  for  Mr.  Roundell  and 
K2 


226  SCIENCE    AND   SENTIMENT. 

Lawrence,  and  there  the  two  young  men  in  due  time  found 
her.  When  they  came  to  the  spot,  however,  although  they 
saw  Miss  Random  upon  the  seat,  they  did  not  see  Jenny 
any  where  near.  As  they  approached  toward  her,  Dome 
nodded  to  them.  Lawrence  bid  her  good  morning,  and 
said, 

"  I  am  very  glad  to  see  you.  How  do  you  do  this  morn- 
ing ?» 

"  Pretty  well,"  said  Miss  Random,  "  only  cross." 

She  said  this  with  something  like  a  pout  upon  her  lips, 
and  something  still  more  like  a  twinkle  in  her  eye.  At 
any  rate,  there  was  something  in  the  expression  of  her  face 
that  led  Lawrence  to  think  that  her  vexation  was  pretended 
rather  than  real. 

"  What  makes  you  feel  cross  ?"  asked  Mr.  Roundell. 

"  Why,  I  came  away  from  home,"  said  Dorrie,  "  and  for- 
got my  India-rubber,  and  so  I  had  to  send  Jenny  back  for 
it,  and  she  has  been  gone  ever  so  long;  and  that  makes 
me  feel  cross  and  contrary.  I  hope  that  one  or  the  other 
of  you  will  say  something  that  I  can  have  a  chance  to  con- 
tradict— especially  Mr.Wollaston,"  she  added,  looking  up 
to  Lawrence  with  a  half  smile  upon  her  face. 

"  Why,  I  thought  you  liked  Mr.Wollaston,"  said  her  cous- 
in, "  or  else  I  should  not  have  brought  him." 

"  I  like  him  well  enough,"  said  Dorrie,  "  if  he  wasn't  so 
dreadfully  scientific." 

"  You  don't  like  science,  then  ?"  said  Mr.  Roundell. 

"No,"  said  Dorrie.  "I  think  it  is  horrid.  It  makes  every 
thing  in  the  world  so  matter-of-fact  like  and  commonplace. 
Look,  now,  at  this  beautiful  stream.  Before  people  knew 
any  thing  scientific  about  it,  what  a  charming  thing  it  was. 
They  followed  it  back  till  they  found  it  coming  out  of  the 
ground  in  a  fountain,  boiling  up  in  a  most  mysterious  and 
wonderful  manner.  They  imagined  it  the  work  of  nymphs 


MISS  RANDOM'S  IDEAS  OF  SCIENCE.  227 

and  naiads,  that  had  magic  power  over  it,  and  gave  all 
sorts  of  wonderful  virtues  to  the  water.  All  its  sparkles 
were  their  smiles,  and  its  ripples,  and  bubbliugs,  and  whirl- 
ings were  their  play,  and  its  murrnurings  and  purlings 
their  fairy  talk.  It  was  all  charming.  But  now  all  this 
is  gone.  The  fountain  is  nothing  but  an  outlet  for  the  rain 
that  has  soaked  down  into  the  ground  among  the  moun- 
tains, with  grass  and  weeds  growing  round  it,  and  the 
stream  itself  only  a  big  drain,  to  drain  off  the  rain-water 
into  the  sea." 

Mr.  Roundell  and  Lawrence  both  laughed  here,  being 
somewhat  amused  at  Miss  Random's  idea  of  the  belittling 
effect  of  scientific  knowledge  in  respect  to  our  conceptions 
of  the  grand  phenomena  of  nature. 

"And  then  thunder  and  lightning,"  continued  Dorrie, 
with  a  triumphant  look  and  tone,  and  turning  toward  her 
cousin.  "  He  explained  it  to  me  the  other  day ;  and  what 
do  you  think  he  made  it  out  to  be  ?  Why,  nothing  but  a 
big  spark  of  electricity,  precisely  such  as  he  makes  by  rub- 
bing a  long  Cologne  bottle  with  a  silk  handkerchief — only 
a  little  larger  and  brighter." 

"A  little  larger  and  brighter?"  repeated  Lawrence,  in  an 
interrogative  tone. 

"  Well,  a  good  deal  larger  and  brighter,  if  you  please," 
said  Dorrie;  "but  just  the  same  thing,  in  fact,  as  any  little 
snap  from  his  electric  machine,  or  like  the  sparkles  we  see 
when  we  rub  a  cat's. back  in  a  dark  closet.  Think  of  mak- 
ing it  out  that  a  bright  flash  of  lightning,  dazzling  your 
eyes  and  setting  the  whole  sky  in  a  blaze,  with  a  tremen- 
dous peal  of  thunder  coming  immediately  after  it,  and 
frightening  you  half  out  of  your  senses,  is  really  nothing 
different  from  the  sparkles  you  see  in  a  silk  stocking  when 
you  take  it  off  in  the  dark." 

Dorrie  said  all  this  in  a  jocose  and  good-humored  way, 


228  SCIENCE    AND   SENTIMENT. 

showing  that  she  was  talking  for  the  sake  of  talking  rather 
than  to  express  any  serious  opinion  that  she  really  enter- 
tained. 

"Now,  you  see,"  she  continued, "before  the  scientific  men 
came  in  to  discover  and  explain  every  thing,  people  often 
had  grand  and  sublime  ideas  in  respect  to  the  wonders  of 
nature,  and  the  sublimity  and  grandeur  were  greatly  in- 
creased by  the  very  mystery  of  them." 

"Yes,"  said  Lawrence,  "that  is  a  very  fair  statement  of 
the  case.  It  is  a  question  between  the  pleasure  of  ignorant 
wonder  and  intelligent  understanding." 

Miss  Random  paused  a  moment  on  hearing  these  words, 
and  seemed  to  be  thinking  of  them. 

"  There  is  one  thing  I  should  like  to  know,  at  any  rate," 
said  Miss  Random,  after  a  moment's  reflection, "  for  I  think 
it  goes  against  your  theory  of  lightning  and  electricity  be- 
ing the  same.  We  get  electric  sparks  most  easily  in  cold 
and  dry  weather,  as,  for  example,  in  cold  and  clear  winter 
nights ;  but  we  never  have  thunder-storms  at  such  times ; 
they  always  come  in  warm  days  and  in  showers  of  rain. 
This  shows  that  they  are  different  things." 

Now  it  is  always  very  important,  when  we  are  convers- 
ing with  persons  younger  than  ourselves,  and  they  ask  a 
question,  to  determine,  before  we  attempt  to  answer  it, 
whether  the  inquiry  which  they  make  is  really  a  request 
for  information  or  an  argument  in  disguise.  If  it  is  really 
a  request  for  information,  your  answer  will  be  listened  to, 
and,  if  satisfactory,  will  be  understood  and  received.  If  it 
is  an  argument  in  disguise,  your  answer  will  scarcely  be 
heard,  and,  if  heard,  will  be  very  little  attended  to.  In  such 
cases,  the  question  is  asked  with  the  expectation  and  hope 
that  it  is  unanswerable,  and  if  you  attempt  to  answer  it, 
the  mind  of  the  person  who  asked  it  is  shut  up  against  re- 
ceiving the  explanation  that  you  give.  It  is  usually  better, 


LAWRENCE'S  FOKBEAKANCE.  229 

therefore,  not  to  attempt  to  answer  such  difficulties  at  all, 
but  to  admit  whatever  of  force,  or  of  seeming  force,  there 
may  be  in  them,  and  leave  the  point  in  question  without 
any  attempt  to  explain  it.  It  is  a  very  difficult  thing  for 
us  to  make  people  see  a  thing  when  they  do  not  wish  to  see 
it,  and  especially  when  their  seeing  it  would  deprive  them 
of  a  triumph  over  us,  which  they  had  anticipated,  and 
would  give  us  a  triumph  over  them. 

Teachers  of  classes  in  Sunday-schools  have  often  occasion 
to  observe  this  distinction,  for  their  pupils  often  ask  them 
questions,  not  from  an  honest  desire  to  have  a  difficulty 
removed,  but  to  show  off  their  own  acumen  in  discovering 
it,  and  pointing  it  out,  and  sometimes  even  with  a  secret 
wish  to  embarrass  and  perplex  the  teacher  with  the  insu- 
perableness  of  it.  Of  course,  a  mind  that  is  in  that  state 
will  receive  no  benefit  from  any  instruction  or  explanation 
offered  to  it,  and  any  attempt  to  offer  instruction  would  be 
vain.  It  would  be  met  by  resistance  more  or  less  open, 
and  the  conversation  would  end  either  in  a  sullen  silence 
on  the  part  of  the  inquirer,  or  in  perfectly  useless  discus- 
sion. 

Now  Lawrence,  like  other  young  men  of  his  age,  some- 
times did  very  foolish  things,  but  he  very  seldom  did  any 
thing  quite  so  foolish  as  to  get  into  a  discussion  of  this 
sort  Avith  a  lady.  So,  when  Miss  Random  argued  that  the 
thunder  and  lightning  of  the  heavens  could  not  be  of  the 
same  nature  as  with  the  electric  cracklings  produced  by 
friction,  from  the  fact  that  the  phenomena  of  the  latter 
kind  are  more  commonly  produced  in  clear,  cold  winter 
weather,  while  the  former  are  almost  entirely  confined 
to  the  hottest  season  of  summer,  and  when,  moreover,  the 
whole  atmosphere  is  filled  with  the  falling  rain,  he  offered 
no  counter  argument  in  reply,  but  rather  fell  in  with  the 
view  which  she  had  expressed. 


230  SCIENCE    AND    SENTIMENT. 

"  That  is  true,"  said  he.  "  I  never  thought  of  it  before 
in  the  precise  light  in  which  you  now  present  it.  Dryness 
and  cold  seem  most  favorable  for  producing  electricity  by 
friction,  while  we  seldom  have  lightning  except  after  a  hot 
day  and  in  the  midst  of  pouring  showers.  Dr.  Franklin 
was  the  man  who  first  proved,  as  he  thought,  that  the  two 
things  were  the  same,  and  if  he  were  alive  now,  and  I  knew 
him,  I  would  go  and  ask  him  what  he  had  to  say  in  respect 
to  that  difficulty." 

Miss  Random  had  been  perfectly  good-humored  in  all 
that  she  had  said,  and  she  was  confirmed  in  this  amiable 
frame  of  mind  by  finding  her  difficulty  treated  with  so 
much  respect. 

While  they  had  been  talking  in  this  way  at  the  seat, 
Theodora's  sister  Jenny,  who  had  been  sent  back  for  the 
India-rubber,  had  returned,  and,  finding  the  party  engaged 
in  conversation,  had  very  discreetly  taken  care  not  to  in- 
.  terrupt  them,  but  had  come  and  laid  the  India-rubber  down 
gently  in  her  sister's  lap,  and  had  gone  down  to  play  on  the 
bank  of  the  stream.  So  Theodora  rose  from  her  seat,  and 
said  that,  as  Jenny  had  come,  they  might  as  well  go  on.* 

"And  when  I  come  to  a  place  where  I  see  any  thing 
pretty  to  draw,"  she  said, "  you  shall  find  or  make  me  a 
seat  somehow,  and  while  I  am  drawing  you  can  go  and 
collect  your  specimens  of  botany  or  geology." 

So  the  whole  party  began  to  walk  on. 

"And  if  you  find  any  pretty  flowers,"  added  Dome,  "you 
may  bring  them  to  me,  only  don't  bring  me  any  of  the  bar- 
barous Latin  names  of  them.  I  don't  see  what  the  use  is 
of  the  Latin  names,  anyhow. 

"Look,  now,  at  that  pretty  little  white  clover,"  she  added, 
pointing  down  to  the  side  of  the  path ;  "  what  do  you  call 
a  white  clover,  now  ?" 

*  See  Frontispiece. 


BOTANICAL   NAMES.  231 

"  The  botanical  name  of  it,  I  believe,  is  trifolium  repens" 
said  Lawrence. 

"  And  what  is  the  use  of  calling  it  by  such  a  name  as 
that  ?"  said  Dorrie.  "  Why  not  call  it  white  clover  and 
done  writh  it  ?  I  am  sure  it  is  a  great  deal  prettier  name 
than  trifolium  repens." 

"That  is  true,"  said  Lawrence.  "I  like  the  name  white 
clover  better  for  some  purposes." 

"  For  what  purposes  ?"  asked  Dorrie. 

"  Why,  when  I  am  talking  about  the  plant  to  farmers  or 
to  children,  because  they  know  it  by  that  name,  and  do 
not  know  it  by  any  other;  but  when  I  am  thinking  of 
the  plant  myself,  I  like  best  to  think  of  it  as  trifolium  re- 
pens,  for  that  is  the  name  that  it  is  known  by  all  the  world 
over.  In  thinking  of  it  by  the  name  that  educated  men 
know  it  by  in  France,  and  Germany,  and  Italy,  and  India, 
I  put  myself,  as  it  were,  in  a  kind  of  relation  to  them,  and 
in  imagination  make  myself  one  of  them,  as  it  were,  and 
form  a  part  of  their  company.  It  is  a  mere  imagination,  I 
admit." 

"  Yes,"  said  Dorrie, "  I  think  it  is." 

"  But  it  is  a  very  pleasant  feeling,  for  all  that.  A  great 
many  of  our  pleasures  are  those  of  the  imagination.  They 
depend  upon  the  form  in  which  ideas  lie  in  our  minds." 

Dorrie  was  silent.  She  felt  that  there  was  some  force 
in  wrhat  Lawrence  was  saying,  but  she  did  not  think  there 
was  much  force  in  it,  after  all. 

"  Well,"  she  said,  presently,  after  a  short  pause, "  you 
must  not  think,  cousin,  that  I  quarrel  a  great  deal  with  Mr. 
Wollaston  about  his  science.  I  think  there  is  some  sense 
in  it." 

She  said  this  with  a  sly  smile  upon  her  face,  which  plain- 
ly indicated  that  she  was  speaking  jocosely. 

"It  is  all  a  question,"  replied  Lawrence, "  as  I  said  be- 


232  SCIENCE    AND   SENTIMENT. 

fore,  between  the  pleasure  of  wondering  ignorance  and  in- 
telligent understanding.  When  a  child  sees  a  magician  put 
a  rabbit  under  a  box,  and  then,  in  a  moment,  lift  the  box 
and  finds  that  Bunny  has  mysteriously  disappeared,  his  as- 
tonishment and  wonder  are  excited,  and  they  are  feelings 
which  give  him  pleasure.  When,  however,  the  manner  in 
which  the  trick  is  performed  is  explained  to  him,  the  won- 
der is  all  gone,  and  another  pleasant  feeling  comes  in  to 
take  its  place — that  of  understanding  the  process  by  which 
the  feat  is  performed.  If,  now,  another  child,  who  knows 
nothing  about  it,  goes  with  him  to  witness  the  performance, 
and  they  sit  together  and  see  the  rabbit  disappear,  one  has 
the  pleasure  of  wondering  at  the  mystery,  and  the  other 
that  of  understanding  the  secret.  I  don't  know  which  you 
would  consider  the  greatest." 

"  I  think  the  pleasure  of  wondering  is  the  greatest,"  said 
Dorrie. 

"Very  likely,"  said  Mr.  Roundell;  "but  the  pleasure  of 
understanding  is  the  highest.  The  child  that  knows  how 
the  trick  is  performed  feels  that  he  stands  on  a  higher 
level  than  the  other,  who  only  wonders  at  the  inexplicable 
mystery  of  it." 

I  think  that  Mr.  Roundell  was  right  in  this  opinion.  It 
is  often  a  very  pretty  thing  for  a  child  to  stand  upon  the 
shore  of  a  brook,  and  see  the  water  flow  by,  and  play  with 
the  pebbles  and  flowers  upon  the  brink.  And  I  do  not 
deny  that  there  may  be  a  certain  feeling  of  pleasure  in  his 
wondering  at  the  mystery  of  such  a  stream,  in  not  knowing 
where  it  comes  from  and  where  it  is  going  to.  But  when 
the  child  is  afterward  taken  to  the  summit  of  a  neighboring 
hill,  and  traces  the  course  of  the  brook  in  its  meanderings 
down  the  mountain  ravines  to  the  place  where  he  had  stood 
upon  the  bank,  and  follows  it  below  as  it  goes  on  gradually 
widening  and  receiving  other  brooklets  on  its  way,  till  it 


MAGICAL   EFFECT   OF   NON-RESISTANCE.  233 

finally  flows  out  into  the  river  or  into  a  lake,  the  pleasure 
which  he  feels  is  of  a  higher  kind,  if  not  greater  in  degree, 
than  that  which  he  felt  before.  His  field  of  view  is  en- 
larged, his  ideas  are  expanded,  and  he  has  raised  himself 
to  a  higher  position,  intellectually,  by  the  new  knowledge 
which  he  has  acquired. 

It  is  substantially  such  a  change  as  this  that  we  pass 
through  at  every  step  we  take  in  becoming  acquainted 
with  the  true  character  and  significance  of  the  natural 
phenomena  which  we  see  taking  place  around  us. 

"  But  you  think,"  said  Mr.  Roundell,  resuming  the  con- 
versation after  a  moment's  pause, "  that  the  pleasure  of 
wondering  about  a  mystery  is  greater  than  that  of  under- 
standing the  explanation  of  it  ?" 

"  Why — no — not  exactly,"  replied  Dora ;  "and  you  must 
not  think  that  I  seriously  have  any  fault  to  find  with 
Mr.Wollaston's  science.  I  like  it  well  enough.  Indeed,  I 
have  learned  a  great  many  things  that  I  like  very  much  to 
know." 

"  She's  a  charming  pupil,  at  any  rate,"  said  Lawrence. 

Dorrie  would  not  have  been  by  any  means  so  ready  to 
make  this  acknowledgment,  which  was,  indeed,  a  half  re- 
traction of  what  she  had  said  before,  if  Lawrence  had  re- 
sisted her,  and  allowed  himself  to  get  into  an  argument 
with  her  on  the  subject.  It  was  one  of  the  numerous  cases 
in  which  the  quickest  and  most  effectual  way  to  disarm 
your  antagonist,  and  lead  him  to  yield,  is  to  cease  your 
resistance  to  him. 

"  I  take  a  much  greater  satisfaction,  for  instance,"  con- 
tinued Miss  Random, "  in  looking  at  the  telegraph  wires 
along  the  roadside  now  that  I  know,  as  Mr.Wollaston  ex- 
plained it  to  me,  that  nothing  passes  along  them,  but  a 
succession  of  impulses — some  kind  of  electrical  impulses. 
I  used  to  think  that  letters  and  words  passed  along  some- 


234  SCIENCE   AND   SENTIMENT. 

how  or  other,  and  I  wondered  how  it  could  possibly  be.  It 
was  nothing  but  ignorant  wonder,  as  Mr.Wollaston  says. 

"  But  he  explained  to  me  that  there  are  really  no  letters, 
or  words,  or  any  thing  of  the  kind  that  pass  along  the  line, 
but  only  a  series  of  electric  pulsations,  in  sets,  each  set  de- 
noting a  particular  letter,  and  they  make  out  the  letters 
and  the  words  at  the  end  of  the  line." 

"  How  do  they  make  them  out  ?"  asked  Mr.  Roundell. 

Mr.  Roundell  was  a  very  intelligent  and  well-informed 
young  man,  but  there  are  a  great  many  intelligent  and 
well-informed  men  who  have  no  clear  idea  of  how  the  elec- 
tric pulses  that  pass  along  the  wires  are  translated  into 
intelligible  words  and  sentences  at  the  end  of  it. 

"  Why,  the  wire  at  the  end  is  coiled  round  an  iron  rod," 
said  Miss  Random,  "  and  every  time  a  pulsation  passes  it 
it  makes  the  rod  a  magnet,  and  it  pulls  a  little  clapper, 
and  the  instant  that  the  flow  is  past  it  lets  the  clapper 
drop  again,  and  so,  by  hearing  or  seeing  the  motions  of  the 
clapper,  they  know  what  sets  of  pulsations  are  passing,  and 
so  can  make  out  the  letters  and  words." 

"  I  should  think  it  would  be  very  difficult,"  said  Mr. 
Roundell. 

"It  is  very  difficult,"  replied  Lawrence, " and  it  requires 
a  great  deal  of  instruction  and  a  great  deal  of  practice  to 
make  a  good  telegraphic  operator." 

"  But  there  is  one  thing  I  don't  understand,"  asked  Miss 
Random, "  and  that  is,  how  the  electricity  makes  the  iron  a 
magnet  just  by  passing  round  it  through  a  coiled  wire.  It 
is  electricity  in  the  wire,  and  magnetism  in  the  rod.  Does 
the  electricity  turn  into  magnetism,  or  does  it  wake  up  the 
magnetism  that  is  in  the  iron  already,  or  how  ?" 

"  Ah  !"  replied  Lawrence,  "  there  you  pass  beyond  the 
bound  of  our  present  knowledge — at  any  rate  of  mine. 
All  we  know  is  the  fact  that,  in  some  mysterious  way,  a 


LIMITS    OP    HUMAN   KNOWLEDGE.  235 

current  of  electricity,  in  passing  across  a  bar  of  iron,  tends 
to  develop  a  magnetic  force  in  it ;  and  if  it  passes  across 
it  a  great  many  times,  as  it  does  in  being  wound  around  it 
in  a  coil,  the  development  of  magnetism  is  all  the  stronger. 
Nobody  has  found  out  yet  what  the  secret  working  of  the 
process  is." 

"  So  there's  where  the  ignorant  wonder  comes  in  again," 
said  Dorrie. 

"  That's  a  fact,"  said  Lawrence. 

"  I  don't  see,  then,  that  you  gain  much,  after  all,"  said 
Miss  Random. 

"  We  certainly  do  not  gain  any  thing,"  said  Lawrence, 
"  in  the  way  of  reducing  the  number  of  the  subjects  of 
mystery  and  wonder  in  the  phenomena  of  nature  around 
us.  We  gain  the  advantage  of  an  intelligent  understand- 
ing of  some  parts  of  the  process  for  a  certain  distance. 
The  satisfaction  which  this  affords  increases  as  our  inves- 
tigations go  on  and  our  horizon  enlarges.  But  we  are  sure 
in  the  end,  whatever  the  path  which  we  follow,  to  find  our- 
selves on  the  verge  of  a  region  of  mystery  and  wonder 
that  we  can  not  penetrate.  Intelligent  understanding  is 
better,  as  far  as  we  can  go  with  it ;  but,  in  whatever  di- 
rection we  may  go.  we  are  sure  to  come  to  a  region  where 
there  is  nothing  for  us  but  wondering  ignorance  at  last." 


236  THE  SUN. 


CHAPTER  XIV. 


THERE  is  perhaps  no  case  in  which,  in  our  attempts  to 
investigate  the  phenomena  of  nature  around  us,  we  are 
brought  sooner  into  the  condition  of  wondering  ignorance 
than  that  of  the  sun.  We  know  it,  it  is  true,  as  the  source 
of  almost  all  the  forces  of  every  kind  which  we  see  in  op- 
eration in  the  earth  around  us.  This  force  comes  from  it 
in  a  perpetual,  an  enormous,  and,  apparently,  an  undimin- 
ished  supply;  but  on  the  principles  now  admitted,  that 
force  can  not  be  increased  or  diminished,  and  can  by  no 
possibility  come  into  existence  out  of  nothing,  the  question 
at  once  arises,  What  is  the  source  of  this  supply  ? 

And  here  we  have  to  enter  at  once  into  the  region  of  ig- 
norant wonder  that  Lawrence  and  Miss  Random  spoke  of 
in  their  conversations;  for  it  is  a  remarkable  fact  that, 
though  the  sun  may  perhaps  be  considered  as  in  some  sense 
the  most  conspicuous  object  in  nature,  and  the  most  open 
to  the  observation  and  even  to  the  full  scrutiny  of  man, 
it  is  yet  the  object  which  of  all  others  is  involved,  in  re- 
spect to  its  constitution  and  the  character  of  the  various 
phenomena  which  it  presents,  in  the  most  absolute  and  im- 
penetrable mystery. 

The  point,  however,  which  we  have  to  consider  in  this 
chapter  is  simply  whence  the  sun  derives  the  enormous 
supply  of  force  which  he  is  now  and  has  long  been  radia- 
ting. The  quantity  of  this  force,  like  most  of  the  quanti- 
ties with  which  astronomy  and  other  sciences  connected 
with  it  are  concerned,  wholly  transcends  the  powers  of  hu- 


SOLAR   RADIANCE    INTERCEPTED   BY   THE    EARTH.      237 

man  conception,  so  that  the  numerical  statements  concern- 
ing them  are  rather  matters  of  curiosity  than  means  of 
conveying  any  definite  ideas  to  the  mind. 

The  distance  of  the  earth,  then,  from  the  sun  being  about 
ninety  millions  of  miles,  the  sun's  rays  must,  of  course,  be 
diffused  at  that  distance  over  the  surface  of  a  sphere  one 
hundred  and  eighty  millions  of  miles  in  diameter,  and  this, 
it  is  found  by  computation,  comprises  an  area  of  thousands 
of  millions  of  millions  of  square  miles — a  space  so  vast 
that  the  portion  of  heat  and  light  which  would  be  inter- 
cepted by  so  small  a  body  as  the  earth  would  be  inconceiv- 
ably minute.  Herschel  made  a  calculation  to  determine 
what  the  proportion  would  be,  and  he  found  that  the  quan- 
tity of  solar  force  received  by  the  earth  was  so  exceeding- 
ly small,  when  compared  with  the  whole  amount  emitted 
by  the  sun,  that  the  fraction  expressing  it  conveys  no 
idea  to  the  mind  of  the  general  reader.  The  fraction  is 

UTTT.oo  0,0  o  o- 

What  an  enormous  reservoir  of  power,  then,  the  sun 
must  contain,  if  so  exceedingly  minute  a  portion  of  it  can 
produce  all  the  effects  which  we  see  taking  place  around 
us  on  the  globe  ! 

And  thus,  while  it  is  very  difficult  for  us  to  comprehend 
how  extremely  minute  a  portion  of  the  solar  force  falls 
upon  the  earth  relatively  to  the  whole  amount  emitted,  it 
is  equally  difficult  to  appreciate  how  immense  the  amount 
is,  absolutely,  that  the  earth  does  thus  receive.  The  most 
careful  observations  and  calculations  have  been  made  to 
determine  this  amount,  and  it  has  been  ascertained  that 
the  total  quantity  emanating  from  the  sun,  and  received 
and  expended  upon  every  acre  of  the  earth's  surface,  or  in 
the  atmosphere  above  it,  is  equal  to  that  represented  by 
the  continuous  labor  of  one  thousand  horses  ! 

A  large  portion  of  this  force  is  employed  in  evaporating 


238  THE    SUN. 

water  and  producing  changes  in  the  atmosphere.  Another 
large  portion  is  absorbed  by  the  organs  of  vegetation  and 
stored  in  the  tissues  of  plants ;  and  a  third  remains  as  heat 
in  the  surface  of  the  ground,  to  be  radiated  again  into 
space  when  night  comes  or  when  the  season  changes.  But 
no  practical  method  has  yet  been  devised  for  intercepting 
and  utilizing  this  force  at  once  on  its  arrival  by  applying 
it  to  mechanical  purposes.  Many  scientific  men,  however, 
and  especially  the  naval  engineer,  Ericsson,  believe  that 
this  will  some  day  be  done,  and  that  we  shall  then  cease 
to  be  dependent,  as  we  are  now,  on  the  stored  force  of  coal 
received  from  the  sun  in  former  ages. 

Several  experiments  have,  in  fact,  been  made  with  a  view 
to  ascertain  the  present  practicability  of  so  gathering  and 
concentrating  the  solar  radiance  as  to  make  it  applicable 
to  the  purpose  of  driving  machinery ;  such  concentration 
is  necessary;  for,  though  a  force  equal  to  that  of  a  thousand 
horses  is  received  within  the  area  of  an  acre,  that  which 
would  be  included  in  any  small  area,  like  that  occupied  by 
the  fixtures  and  appurtenances  of  a  steam-engine,  would 
be  too  small  to  produce  any  useful  mechanical  effect.  A 
French  mechanician,  however,  succeeded  a  few  years  ago 
in  so  concentrating  the  sun's  rays  by  means  of  reflectors 
as  to  drive  a  small  hot-air  engine  by  the  heat  derived  from 
them. 

Now,  when  we  consider  that  a  force  is  continually  flow- 
ing from  the  sun  equal  to  that  of  a  thousand  horses  on 
every  acre  of  the  earth's  surface,  and  yet  that  the  amount 
that  is  intercepted  by  the  whole  earth  is  only  about  one 
two  hundred  millionth  of  the  quantity  that  is  emitted  by 
the  sun,  and  that  this  immense  emission  has  now  been 
going  on  not  only  for  the  six  thousand  years  of  history, 
but,  as  there  is  every  reason  to  believe,  for  millions  upon 
millions  of  ages  before,  we  see  at  once  that  there  must  be 


DIFFERENT   THEORIES.  239 

some  mysterious  source  of  supply  of  a  magnitude  tran- 
scending all  possible  human  conception.  What  is  the  na- 
ture of  this  source  of  supply  no  one  knows.  In  the  absence 
of  any  thing  like  positive  proof  of  what  the  origin  of  this 
vast  and  inexhaustible  energy  actually  is,  all  the  light  we 
have  upon  the  subject  consists  of  conjectures  and  specula- 
tions as  to  what  it  may  be.  The  principal  theories  that 
have  been  advanced  are  these : 

1.  That  the  sun  is  a  hot  body  cooling. 

2.  That  it  is  a  combustible  body  burning. 

3.  That  it  is  an  inert  mass  heated  and  kept  hot  by  a  suc- 
cession of  blows. 

1.  That  the  sun  is  a  hot  body  cooling.  This  was  the 
most  obvious  thought,  and  the  one  first  adopted.  It  is 
true,  it  only  removed  the  difficulty  one  step  farther  back  ; 
for,  even  if  there  could  be  heat  enough  contained  in  such 
a  mass  as  that  of  the  sun  to  endure  for  so  many  ages,  the 
question  would  arise,  By  what  process  could  such  a  hot 
body  have  been  formed  in  the  centre  of  the  solar  system? 
But  then  this  is  the  final  result  of  all  our  discoveries  and 
explanations  of  natural  phenomena.  We  only  remove  the 
difficulty  one  or  more  steps  back.  We  can  never,  by  mere 
scientific  investigation,  arrive  at  any  beginning. 

This  theory  is,  however,  in  its  original  form,  now  gener- 
ally abandoned ;  for  it  has  been  shown  that  radiation  from 
such  a  mass  at  the  rate  at  which  the  radiation  from  the 
sun  is  now  going  on  would,  according  to  all  known  laws 
of  radiation,  exhaust  the  supply  so  rapidly  as  to  produce  a 
total  change  in  the  effects  of  it  in  the  course  of  a  far  short- 
er period  than  even  the  six  thousand  years  of  history. 

A  theory,  however,  which  is  in  some  respects  a  modifi- 
cation of  this  original  idea,  has  been  recently  advanced, 
and  that  is,  that  the  sun  may  be  a  vast  mass  of  gaseous 
matter — enormously  compressed,  it  is  true,  but  still  retain- 


240  THE   SUN". 

ing  its  gaseous  condition — which  is  in  the  process,  as  it 
cools,  <&  gradually  liquefying.  In  such  a  process  it  would, 
of  course,  give  out  in  radiation  not  only  its  heat  of  temper- 
ature, but  also  its  heat  of  vaporization.  This  is  substan- 
tially the  same  process  that  takes  place  in  warming  a 
house  by  means  of  steam.  The  steam  from  the  boiler  car- 
ries into  the  pipes  not  only  the  heat  of  its  temperature,  but 
also  that  of  its  vaporization,  and  this,  as  well  as  the  other, 
it  gives  out  by  its  condensation  in  the  pipes.  If  it  were 
air  instead  of  steam  that  was  conveyed  into  the  pipes, 
though  it  might  be  of  precisely  the  same  temperature,  it 
would  give  out  comparatively  little  heat,  namely,  only  that 
of  its  temperature — that  is,  the  amount  necessary  to  cool 
it;  but  the  pipes  must  abstract  from  the  steam  not  only 
enough  to  cool  it,  but  also  the  enormous  additional  quan- 
tity necessary  to  condense  it — an  amount  equal,  as  we  saw 
in  a  previous  chapter,  to  not  far  from  a  thousand  units  to 
the  pound. 

This  supposition,  that  the  body  of  the  sun  is  composed 
of  a  gas  in  the  process  of  being  liquefied  by  the  radiation 
of  both  its  sensible  and  latent  heat,  would  account  for  the 
continuance  of  the  radiation  for  an  immensely  longer  pe- 
riod than  would  be  required  for  the  cooling  of  a  body  with- 
out any  change  of  state,  but  the  origin  of  the  supply  would 
remain  as  great  a  mystery  as  ever. 

2.  The  second  of  the  three  theories  I  have  named  is  that 
the  sun  is  a  combustible  body  burning. 

Now  combustion  is  the  name  we  give  to  certain  kinds 
of  chemical  action  so  intense,  in  respect  to  the  degree  of 
force  with  which  the  elements  concerned  come  together, 
as  to  produce  an  abundant  evolution  of  light  and  heat — 
that  is,  offeree  in  those  forms.  Now  the  quantity  offeree 
thus  liberated  is  that  which  has  been  already  described  as 
the  heat  of  dissociation,  which,  as  we  have  seen,  is  vastly 


GREAT    I1EAT   PRODUCED   BY    COMBUSTION.  241 

greater  than  that  of  vaporization ;  that  is,  the  heat  re- 
quired for  separating  the  particles  of  water  from  each  oth- 
er so  as  to  convert  the  substance  from  the  liquid  to  the 
gaseous  state,  though  very  great,  is  enormously  surpassed 
by  that  required  for  separating  the  particles  of  oxygen  and 
hydrogen  from  each  other  in  decomposing  the  water.  It 
requires,  as  we  have  seen,  nearly  1000  units  of  heat  per 
pound  to  vaporize  water,  and  something  like  50  or  60  thou- 
sand to  separate  the  particles  of  the  vapor  into  their  orig- 
inal elements.  Thus,  instead  of  regarding  the  sun  as  a  hot 
body,  cooling  itself  by  radiating  its  sensible  and  its  latent 
heat — giving  out  in  the  latter  its  heat  of  vaporization — 
this  second  theory  views  it  as  a  combustible  body  burning ; 
that  is,  as  a  mass  of  different  substances  having  so  strong 
a  chemical  affinity  for  each  other  that  they  combine  with 
great  intensity  of  action,  so  as  to  give  out,  in  the  form  of 
light,  heat,  and  actinism,  the  whole  of  the  immense  force 
required  to  separate  such  substances  in  decomposition,  and 
thus  provides  an  immensely  more  copious  source  of  sup- 
ply. By  this  latter  supposition  a  vastly  greater  and  more 
enduring  heat  is  provided  for  than  by  the  former,  just  as  a 
mass  of  coal  in  burning  will  give  out  a  vastly  greater  quan- 
tity of  heat  than  a  mass  of  iron  would,  of  the  same  weight, 
in  simply  cooling  from  the  same  temperature. 

But  the  quantity,  after  all,  would  not  be  enough  to  ac- 
count for  so  long-continued  and  so  enormous  a  supply  of 
force  as  that  which  has  been  coming  for  so  many  ages  from 
the  sun.  The  most  careful  calculations  have  been  made, 
and  it  has  been  shown  conclusively  that  if  the  sun  were  a 
mass  of  coal,  the  combustion  of  it  would  not  afford  force 
enough  to  account  for  the  solar  radiation  for  but  a  very 
small  portion  of  the  long  period  during  which  we  know 
that  the  sun  has  been  shining  with  at  least  the  present  fer- 
vency of  its  beams. 

L 


242  THE   SUN. 

3.  The  third  theory  which  has  been  advanced  is  that  the 
sun  is  an  inert  mass  kept  hot  by  a  perpetual  succession  of 
blows.  These  blows  are  supposed  to  be  given  by  masses 
of  meteoric  or  other  matter  constantly  falling  upon  it,  and 
striking  with  prodigious  violence  as  they  fall. 

It  has  been  shown  in  a  former  chapter  that  whenever 
two  masses  of  matter  strike  each  other,  the  extinguishment 
of  the  motion  thus  resulting  is  accompanied  by  a  develop- 
ment of  heat,  and  also,  when  the  collision  is  sufficiently  vi- 
olent, of  light,  and  perhaps  of  electricity,  and  of  other  forms 
of  energy.  Thus  a  blacksmith  can  heat  a  bar  of  iron  red 
hot  by  simply  hammering  it  upon  an  anvil,  and  a  ball 
from  the  gun  of  a  siege  train,  when  it  strikes  the  wall  of 
the  fort  attacked,  is  so  heated  by  the  sudden  extinction  of 
its  motion  as  at  night  to  emit  a  flash  of  light  that  is  plain- 
ly visible.  It  is  calculated  that  the  heat  produced  by  the 
impact  of  a  leaden  bullet  upon  a  solid  wall  would  be  suffi- 
cient to  melt  the  lead,  if  it  could  all  be  imparted  to  the 
bullet,  instead  of  being  divided  between  the  bullet  and  the 
wall. 

Nor  does  it  make  any  difference  in  the  proportional  ef- 
fect whether  the  bodies  impinging  against  each  other  are 
large  or  small,  or  whether  the  force  with  which  they  strike 
is  violent  or  gentle.  The  quantity  of  heat  which  is  evolved 
depends  simply  upon  the  quantity  of  motion  extinguished, 
so  that  a  flake  of  snow  descending  ever  so  gently  upon  the 
grass,  and  stopped  by  the  collision,  warms  itself  and  the 
grass  by  the  extinction  of  its  motion,  just  as  much,  in  pro- 
portion to  its  weight  and  the  velocity  of  its  descent,  as  a  500- 
pound  iron  ball  in  crashing  against  an  iron-clad  wall  of  ma- 
sonry. 

Now  there  is  every  reason  for  believing  that  the  region 
of  space  included  within  the  preponderating  influence  of 
the  sun,  and  within  which  the  planets  move,  is  very  far 


FOREIGN   BODIES   FALLING   INTO   THE   STJN.  243 

from  being  occupied  solely  by  these  visible  orbs.  The  hun- 
dreds of  minor  planets  that  have  recently  been  discovered, 
the  thousands  of  millions  of  meteors  and  comets — for  a  dis- 
tinguished astronomer  proved  that  there  were  more  comets 
in  the  space  within  the  influence  of  the  sun  than  there  were 
sands  upon  the  sea-shore — show  that  there  is  revolving 
about  the  sun  at  all  times  a  quantity  of  matter,  in  various 
forms,  wholly  inconceivable  in  amount.  And  if  the  space 
through  which  these  masses  move  is  filled,  as  there  is  every 
reason  for  believing  that  it  is,  with  some  resisting  medium, 
they  must  be  gradually  drawn  nearer  and  nearer  to  the 
sun  in  their  orbits  of  revolution,  and  there  must  be  all  the 
time  vast  numbers  of  them  falling  into  it,  and  in  thus  fall- 
ing into  it,  their  motion,  by  its  extinction,  must  be  convert- 
ed into  heat.  The  only  question  would  seem  to  be  wrheth- 
er  there  can  be  a  sufficient  quantity  of  such  matter  falling 
into  the  sun  to  develop,  by  the  resulting  concussion,  the 
quantity  of  heat  necessary  to  supply  the  enormous  emana- 
tions. 

There  is  one  important  thing  to  be  considered  in  respect 
to  this  point,  and  that  is,  that  it  makes  no  difference  in  re- 
gard to  the  amount  of  heat  that  would  be  evolved  by  a 
body  falling  upon  the  sun,  whether  it  strikes  upon  a  solid 
surface  or  plunges  into  a  liquid  or  a  gaseous  one,  for  we 
may  even  suppose  the  sun  to  be  composed  of  a  gaseous  sub- 
stance enormously  compressed.  In  the  case  of  a  solid,  the 
motion  would  be  almost  instantaneously  extinguished.  In 
the  case  of  the  foreign  body  plunging  into  a  liquid  or  a 
gas,  the  extinction  of  the  motion  would  be  more  gradual; 
but  in  both  cases  the  amount  of  extinction  of  motion,  and 
the  whole  quantity  of  heat  resulting  from  it,  would  be  the 
same ;  only,  in  the  former  case,  the  heat  would  be  more 
suddenly  produced,  and  would  appear  more  directly  at  the 
spot  on  the  surface  where  the  impingement  took  place, 


244  THE    SUN. 

whereas  in  the  other  it  would  be  more  gradually  devel- 
oped, and  would  be  diffused  more  generally  through  the 
mass. 

Another  thing  to  be  considered  is  that  a  body  falling 
into  the  sun  would  fall  with  a  very  much  greater  force 
than  one  descending  from  a  corresponding  height  upon  the 
earth ;  for,  on  account  of  the  immense  mass  of  the  sun,  the 
effect  of  gravitation  on  its  surface  is  between  twenty  and 
thirty  times  as  great  as  that  exercised  at  the  surface  of  the 
earth;  so  that  the  force  with  which  a  falling  body  would 
strike — that  is,  the  amount  of  motion  that  would  be  ex- 
tinguished by  the  collision — and,  consequently,  the  amount 
of  heat  that  would  be  generated,  would  be  vastly  greater 
than  that  which  would  be  produced  by  the  fall  of  a  simi- 
lar body  upon  the  surface  of  the  earth. 

Now  the  most  laborious  calculations  have  been  made  by 
certain  German  mathematicians  and  astronomers,  based  on 
very  careful  and  long-continued  observations,  to  determine 
what  the  probability  is  in  respect  to  the  quantity  of  mat- 
ter that  is  thus  continuously  arriving  at  and  falling  into 
the  sun,  the  velocity  with  which  it  would  be  moving  at  the 
time  of  collision,  and  the  quantity  of  heat  which  would  be 
developed,  and  the  result  is  very  strongly  confirmative  of 
the  theory  in  the  minds  of  a  great  number  of  scientific  men. 
It  has  been  shown  by  very  careful  computations  that  the 
velocity  with  which  a  revolving  body,  large  or  small,  would 
ultimately  sink  into  the  sun,  would  be  not  less  than  400 
miles  in  a  second,  and  that  the  quantity  of  matter  that 
would  be  required  to  maintain  the  present  radiation  from 
the  sun  for  2000  years  would  form  a  layer  upon  his  surface 
of  less  than  twelve  miles  in  thickness,  which  would  increase 
the  diameter  of  that  orb  by  an  amount  that  would  be  whol- 
ly imperceptible  under  the  nicest  observations  at  this  dis- 
tance. 


(5ORUSCATIONS   AROUND  THE   SOLAR   DISK.  245 

There  are,  however,  many  scientific  men  who  are  far 
from  being  satisfied  with  this  explanation,  so  that  the  ques- 
tion must  be  considered  as  still  in  doubt.  All  we  have  to 
do  at  present,  therefore,  is  to  make  ourselves  acquainted 
with  such  facts  in  regard  to  the  constitution  and  condition 
of  the  sun  as  have  been  observed,  and  hold  our  minds 
somewhat  in  suspense  in  regard  to  the  true  explanation  of 
the  phenomena  until  more  light  shall  be  obtained. 

It  is  well  ascertained  that  it  is  only  the  central  and 
brighter  portion  of  this  body  which  is  directly  observable 
by  us,  and  this  gives  it  the  appearance  of  a  well-defined 
spherical  mass,  excessively  brilliant,  but  in  a  state  of  calm- 
ness and  repose.  But  it  has  been  found  within  a  few  years, 
and  especially  by  means  of  observations  during  periods  of 
total  eclipse,  when  the  whole  of  this  central  portion  is  con- 


246  THE   SUN. 

cealed  from  view,  that  instead  of  having  a  distinct  and  de£ 
inite  quiescent  boundary,  the  whole  vicinity  of  what  has 
been  supposed  to  be  the  boundary  is  filled,  to  the  height 
of  many  thousands  of  miles,  with  a  boiling,  flaming,  furious 
mass,  in  a  state  of  the  most  intense  and  violent  action. 

And  the  indications  of  this  and  similar  action  are  seen 
extending  themselves  over  the  whole  surface  of  the  orb, 
which  seems  to  be  furrowed  with  incandescent  billows  in 
a  state  of  incessant  motion.  Enormous  flame-like  corus- 
cations, in  masses  larger  than  this  globe  on  which  we  dwell, 
rise,  and  glow,  and  wave,  and  then  melt  away  and  disap- 
pear. Some  of  these  blazing  radiations  appear  to  project 
themselves  forty  or  fifty  thousand  miles  into  the  surround- 
ing space,  though,  on  account  of  the  immense  magnitude 
of  the  body  of  the  sun,  and  his  vast  distance  from  us,  they 
do  not  perceptibly  affect  the  smoothness  of  the  contour  of 
his  disk,  as  it  appears  from  the  earth  to  our  unassisted  vis- 
ion ;  but  the  real  violence  and  rapidity  of  the  action  thus 
taking  place  are  inconceivable.  On  the  one  hand,  cavities 
of  appai'ently  absolute  darkness,  and,  on  the  other,  vast  pro- 
tuberances of  extraordinary  and  special  brightness,  form 
and  fluctuate  over  the  surface,  increasing  and  diminishing 
at  the  rate  of  thousands  of  miles  in  extent  in  very  brief 
periods  of  time. 

Thus  the  sun,  instead  of  existing  in  the  calm,  placid,  and 
unchanging  condition  which  it  appears  to  assume,  is  in  re- 
ality a  mass  of  seething  and  surging  incandescence,  deform- 
ed by  incessant  and  tempestuous  agitations  of  surface,  pro- 
duced by  contests  among  forces  the  nature  of  which  elude 
our  research  as  completely  as  the  enormous  magnitude  and 
extent  of  their  effects  surpass  our  powers  of  conception. 

Among  all  the  phenomena  denoting  the  incessant  dis- 
turbance and  change  which  is  taking  place  in  the  condition 
of  the  solar  surface,  what  are  known  as  the  spots,  or  mac- 


MACULAE   AND   FACUL^E.  247 

tt&e,  as  they  arc  termed  by  astronomers,  which  are  some- 
times large  enough  to  be  seen  by  the  naked  eye,  first  at- 
tracted the  attention  of  mankind,  and  have  been  a  very 
fruitful  subject  of  speculation  in  all  ages.* 

It  was  for  some  time  a  matter  of  doubt  whether  the  ap- 
pearance of  spots  was  due  to  something  actually  attached 
to  and  forming  a  part  of  the  sun's  surface,  or  whether  they 
were  caused  by  opaque  bodies  revolving  in  space  at  a  dis- 
tance from  the  sun,  and  passing  across  his  disk  from  time 
to  time,  so  as  to  intercept  a  portion  of  his  light.  That  the 
former  supposition  was  the  true  one  soon  seemed  to  be 
proved  by  the  fact  that  when  the  spots  disappear  on  one 
side,  and  then  afterward  reappear  again  on  the  other,  which 
often  happens,  the  interval  of  disappearance  is  always  the 
same  as  the  time  that  they  continue  in  sight.  This  evi- 
dently could  not  be  the  case  if  the  phenomena  were  due  to 
bodies  revolving  at  a  distance  from  the  sun,  since  it  would 
be  only  a  small  portion  of  the  orbit  of  such  bodies  that 
would  come  between  us  and  the  disk  in  the  course  of  its 
revolution,  and,  consequently,  the  times  of  appearance  and 
disappearance  would  be  very  unequal. 

The  spots  on  the  sun  are  sometimes,  though  not  very  oft- 
en, of  such  magnitude  that  they  can  be  seen  by  the  naked 
eye.  To  make  it  possible  to  look  directly  at  the  dazzling 
surface,  astronomers  employ  darkly-colored  glasses  to  in- 
tercept a  portion  of  the  rays.  By  ordinary  observers,  glass 
covered  with  a  film  of  smoke,  by  being  held  in  the  flame 
of  a  lamp  or  candle,  is  used. 

The  smoked  glass  answers  the  purpose  sufficiently  well 
for  sudden  and  temporary  emergencies ;  but  for  permanent 
use  astronomers  employ  a  helioscope,  which  is  much  more 

*  In  addition  to  the  macula,  there  are  certain  lines  of  superior  and  ex- 
cessive brilliancy  often  seen  in  the  vicinity  of  the  spots,  which  are  termed 
faculce,  from  a  Latin  word  signifying  a  small  torch. 


248  THE   SUN. 

convenient.  This  instrument  consists  of  two  wedge-shaped 
plates  of  glass — one  of  a  very  dark  color,  and  the  other 
perfectly  transparent — made  to  fit  each  other  very  exactly, 

and  set  together  in 
a  suitable  frame,  as 
shown  in  the  en- 
graving. The  frame 
is  rectangular  in 
form,  and  of  a  width 
and  length  conven- 

TUB  IIKLIOSOOPK.  jent     foj.      ^Q      Q  y  g  ^ 

and  is  provided  with  a  handle.  The  plates  of  glass  are  so 
fitted  together  (as  shown  in  the  second  figure,  which  pre- 
sents a  sectional  view  of  them)  that  the  thick  part  of  one 
plate,  ABC,  lies  upon  the  thin  part  of  the  other,  CBD. 
The  thickness  of  the  glass,  therefore,  through  which  the 
rays  have  to  pass  is  the  same  every  where,  and  there  is, 
therefore,  no  refraction  to  distort  the  image,  while  by  mov- 
ing the  instrument  along  before  the  eyes  the  image  may 
be  made  more  bright  or  more  obscure  at  pleasure.  At  SE, 
for  example,  the  rays  pass  through  a  greater  portion  of  the 
dark  glass  than  at  S'E'. 

These  simple  contrivances  answer  very  well  for  viewing 
the  sun  with  the  naked  eye;  but  great  difficulties  have 
been  encountered  by  astronomers  in  devising  effectual  and 
convenient  means  of  enfeebling  the  rays  in  the  use  of  pow- 
erful telescopes.  Some  kinds  of  colored  glass,  it  was  found, 
intercepted  the  rays  of  light,  but  allowed  the  heat  to  pass 
freely ;  while  others,  which  absorbed  the  heat,  did  not  sen- 
sibly diminish  the  dazzling  intensity  of  the  light.  With- 
out great  care,  moreover,  the  plate  or  plates  of  colored 
glass,  by  a  more  or  less  irregular  refraction  of  the  rays,  af- 
fected unfavorably  the  distinctness  of  the  image. 

These  difficulties  have  at  length  been  in  part  avoided 


SPOTS   ON  THE   SUN. 


249 


and  in  part  overcome  in  the  use  of  an  arrangement  by 
which  a  magnified  image  of  the  sun  is  received  upon  a 
white  screen,  like  the  picture  in  a  camera  obscura,  where  it 
can  be  studied  in  all  its  aspects  and  peculiarities  by  the 
observer  at  his  leisure,  and  drawings  and  photographs  taken 
with  great  facility. 

The  spots,  some  of  which  are  almost  always  to  be  seen 


GENERAL   Al'I'EAKANCK   OF   THE  SPOTS. 

L2 


250 


THE    SUN. 


by  means  of  powerful  telescopes,  are  of  the  most  fantastic 
forms ;  but,  with  few  exceptions,  each  one  consists  of  an 
apparently  black  central  portion,  surrounded  by  a  gray  or 
semi-luminous  border,  which  is  called  the  penumbra ;  and 
usually,  like  clouds  floating  in  the  sky,  they  change  their 
form  from  day  to  day  as  they  are  borne  slowly  along  by 
the  revolution  of  the  sun.  They  are  sometimes  small  and 
circumscribed  in  form,  at  others  extremely  irregular, 
spreading  into  the  most  fantastic  forms,  but  always,  or 
nearly  always,  bordered  by  the  penumbra. 

Many  of  these  spots,  though  occupying  but  a  small  space 
apparently  upon  the  sun's  disk,  are  really  of  immense  mag- 
nitude. Vast  numbers  of  them  are  so  large  that  if,  as  has 
often  been  supposed,  they  are  cavities  in  a  luminous  enve- 
lope surrounding  the  sun,  a  body  of  the  magnitude  of  this 
earth  might  be  dropped  into  them  without  touching  the 
sides ;  and  some,  that  have  been  observed  and  measured, 
would  admit  in  this  manner  bodies  of  from  fifty  to  a  hun- 
dred times  the  bulk  of  this  globe. 

The  evidence  which  led  many  astronomers  to  conclude 


APPEARANCES   INDICATING   CAVITIES. 


THE    PHOTOSPHERE.  251 

that  the  spots  are  of  the  nature  of  cavities,  and  not  of  pro- 
tuberances upon  the  surface  of  the  sun,  is  derived  from  cer- 
tain peculiar  changes  in  the  form  of  the  spot,  which  take 
place  as  it  passes  away  from  the  centre  of  the  disk,  where 
it  is  presented  directly  to  view,  toward  the  limb,  where  it 
is  seen  obliquely.  These  changes  are  rudely  represented 
in  the  preceding  engraving. 

It  is  plain  that  if  the  spots  were  protuberances — the  pe- 
numbra surrounding  them  forming  the  sides — the  portion 
of  the  penumbra  lying  to  the  right  of  the  spot  would  grad- 
ually become  concealed,  while  that  on  the  left  side  would 
come  more  and  more  directly  into  view,  as  the  spot  moved 
from  the  centre  toward  the  right  limb  of  the  sun  as  view- 
ed by  the  spectator.  The  contrary  is,  however,  generally 
found  to  be  the  fact,  as  shown  in  the  engraving.  This 
phenomenon  is  often  referred  to  as  proving  satisfactorily 
that  the  spots  are  of  the  nature  of  cavities  opening  in  some 
kind  of  bright  gaseous  or  liquid  envelope  surrounding  the 
sun,  and  disclosing  a  view  of  something  dark,  or  at  least 
of  something  having  the  effect  of  a  dark  object  on  our  vis- 
ion. It  is  not,  however,  considered  absolutely  certain  that 
there  is  not  some  illusion  about  these  appearances.  How- 
ever this  may  be,  the  vast  luminous  envelope  which  the 
sun  presents  to  our  view,  endued  with  such  exceeding  bril- 
liancy, and  in  a  state  of  the  most  intense  and  violent  com- 
motion, is  the  source  from  which  the  heat  and  light  that 
emanate  from  the  sun  seem  to  be  derived,  and  is  called  the 
photosphere. 

The  photosphere,  as  this  supposed  igneous  envelope 
forming  the  radiant  surface  of  the  sun  is  called,  is  popu- 
larly conceived  of  as  existing  in  a  calm,  tranquil,  and 
unchanging  condition,  though  constantly  pouring  forth 
streams  of  heat  and  light  of  such  intense  and  dazzling  bril- 
liancy. As  seen  without  any  scientific  aids  to  the  vision, 


252  THE   SUN. 

this  is  the  aspect  which  it  presents;  but,  when  viewed 
through  powerful  telescopes,  this  seeming  quiescence  and 
uniformity  disappears,  and  the  whole  surface,  as  has  al- 
ready been  said,  is  found  to  be  in  a  state  of  the  most  vio- 
lent action  and  agitation.  The  surface  becomes  variega- 
ted, too,  by  forms  and  figures  of  different  degrees  of  bril- 
liancy, which  are  continually  varying  in  contour  and  posi- 
tion, and  melting  into  each  other  in  changes  which,  to  be 
seen  at  all  at  such  a  distance,  must  be  produced  by  move- 
ments of  enormous  magnitude,  and  of  vast  rapidity  of  ac- 
tion. The  general  surface  is  every  where  mottled  with  a 
kind  of  brilliant  efflorescence,  and  in  the  vicinity  of  the 
spots  a  mysterious  configuration  appears  called  the  willow 
leaves,  from  the  resemblance  to  a  group  of  willow  leaves 
lying  on  the  ground.  In  some  parts  these  leaves  lie  min- 
gled confusedly,  crossing  each  other  in  every  direction.  In 
other  parts,  especially  in  the  penwnbrce  of  the  spots,  there 
is  a  tendency  to  regular  arrangement,  and  especially  to  a 
convergent  direction  toward  the  centre  of  the  spot.  Some- 
times lines  of  these  figures  extend  out  across  a  spot,  form- 
ing what  Nasmyth,  the  astronomer  who  first  observed 
them,  named  luminous  bridges.  The  engraving  represent- 
ing these  appearances  is  not  a  fancy  sketch,  but  an  exact 
copy  of  a  group  of  spots,  and  of  the  surrounding  surface 
of  the  sun,  as  seen  by  Nasmyth  on  the  5th  of  June, 
1864. 

The  mottled  appearance  of  the  photosphere,  as  observed 
by  the  aid  of  the  most  powerful  telescopes,  is  still  more 
distinctly  shown  in  the  next  engraving,  which  records  an 
observation  made  by  Huggins.  The  granulations  of  light 
which  form  the  mottling  of  the  surface  are  of  a  form  some- 
what resembling  grains  of  rice,  to  which  they  have  some- 
times been  compared,  and  are  very  curiously  grouped.  The 
nature  and  the  cause  of  them,  as  of  every  thing  else  re- 


MOTTLED  SUBFACE.      WILLOW   LEAVES.      LUMINOUS  BBIDOI 


CHANGES   IN   THE    SPOTS. 


255 


lating  to  the  physical  constitution  of  the  sun,  is  enveloped 
in  unfathomable  mystery. 

It  is  remarkable  that  the  spots  in  the  sun  do  not  appear 
indiscriminately  in  all  parts  of  the  disk ;  they  are  chiefly 
confined  to  a  zone  extending,  some  30°  or  40°  on  each  side 
of  the  equator. 

It  is  true  that  those  existing  at  a  distance  from  the  equa- 
tor toward  either  pole  would  be  seen  more  or  less  oblique- 
ly, and  would  consequently  come  less  distinctly  into  view. 
The  smaller  ones,  situated  far  to  the  northward  or  south- 
ward, might,  from  this  cause,  especially  if  it  should  be  true 
that  the  spots  are  of  the  nature  of  excavations  or  openings 
in  a  liquid  or  gaseous  envelope,  entirely  escape  observa- 
tion ;  but,  making  all  necessary  allowances  for  this,  it  re- 
mains certain  that  the  spots  are  due  to  some  action  among 
the  constituents  of  the  sun  which  is  mainly  confined  to  the 
equatorial  regions  of  his  surface. 


Spot  as  seen  Oct.  13, 1865.  Spot  as  seen  Oct.  14, 1865. 

CHANGES  OV  FORM. 


256  THE    SUN. 

The  changes  of  form  and  the  movements  of  the  spots 
may  be  very  exactly  observed  and  recorded  by  means  of 
cross-lines  in  the  field  of  view  of  the  telescope.  The  en- 
gravings representing  this  mode  of  observation  show  the 
changes  of  form  and  position  of  a  spot  which  passed  over 
the  disk  of  the  sun  in  the  fall  of  1865,  from  drawings  made 
by  the  English  astronomer  Howlet.  On  the  upper  margin 
of  each  figure,  the  divisions,  in  seconds,  are  marked  for  one 
angular  minute  of  the  surface ;  and  by  noting  the  relation 
of  the  spot  to  these  marks,  and  to  the  lines  drawn  through 
them,  the  reader  will  perceive  the  changes,  both  in  the 
forms  of  the  spots  and  in  their  position,  on  the  different 
days  specified.  It  has  been  shown,  by  careful  observations 
made  in  this  manner,  that  the  spots  do  not  occupy  a  fixed 
position,  as  if  pertaining  to  any  solid  portion  of  the  orb, 
but  that  they  have  a  comparatively  slow  motion  upon  the 
surface  of  it,  as  well  as  a  motion  with  the  surface  in  its  reg- 
ular rotation. 

These  changes  of  form  and  position,  not  only  of  the  dark 
spots,  but  also  of  the  bright  lines  and  spaces  which  diver- 
sify the  general  surface  of  the  sun,  though  seemingly  grad- 
ual and  slow,  as  they  appear  to  us  at  the  enormous  dis- 
tance from  which  we  view  them,  are  really  effected  with 
prodigious  rapidity,  and  imply  a  continual  and  inconceiv- 
ably intense  action  of  some  nature  or  other  among  the 
constituents  of  the  photosphere. 

But  the  most  striking  proofs  of  the  prodigious  intensity 
of  the  action  which  is  taking  place  in  the  sun,  and  the  enor- 
mous magnitude  of  the  movements  induced  by  it,  are  af- 
forded, as  has  already  been  said,  by  the  views  which  are 
presented  at  the  time  of  a  total  eclipse.  If  the  surface  of 
the  orb  were  really  bordered  by  the  smooth,  well-defined, 
and  quiescent,  though  dazzling  envelopment  which  it  seems 
to  present  to  view  in  ordinary  vision,  the  intervention  of 


CORUSCATIONS  AND   COKON^E.  257 

the  moon,  when  the  disk  was  entirely  covered,  would  com- 
pletely suppress  the  light  from  it  during  the  brief  period 
of  totality,  and,  as  it  were,  blot  it  out  entirely  from  the 
heavens.  But  this  is  far  from  being  the  case.  Although 
the  whole  body  of  the  sun  is  covered,  the  figure  of  the 
moon  intervening  is  surrounded  by  a  remarkable  halo  of 
bright  light,  with  protuberances,  and  radiations,  and  corus- 
cations breaking  out  on  every  side,  like  vast  volcanoes,  or, 
rather,  like  rolling  mountains  of  liquid  fire. 

These  incandescent  emanations  are  observed  to  be  in  a 
state  of  incessant  movement.  The  changes  of  form  and 
position  are,  of  course,  as  seen  from  this  enormous  distance, 
apparently  slow;  the  actions,  however,  in  reality,  take  place 
on  an  inconceivably  vast  scale,  and  with  enormous  power 
and  rapidity.  In  one  instance  an  extremely  brilliant  cor- 
uscation was  observed  to  surge  across  the  disk  at  a  rate 
which  carried  it,  in  the  space  of  five  minutes,  over  a  dis- 
tance of  more  than  thirty  thousand  miles.  How  inconceiv- 
ably vast  must  be  the  force  of  an  agency  which  such  a 
movement  as  this  implies ! 

These  coruscations  and  corona?,  formed  of  luminous  em- 
anations rising  high  above  the  surface  of  the  sun,  were  ob- 
served very  distinctly  during  the  eclipse  of  the  year  1869, 
and  more  perfect  and  exact  representations  of  them  were 
secured  than  has  ever  been  possible  before,  on  account  of 
the  very  complete  arrangements  for  photographing  the 
eifects  which  the  observers  had  made.  In  various  parts  of 
the  margin  of  the  disk,  rose-colored  protuberances,  like 
surging  waves  of  fire,  and  coruscations  shooting  out  for 
thousands  of  miles,  like  gigantic  jets  of  flame,  were  seen 
by  the  eye  and  photographed  by  the  instruments. 

In  addition  to  the  knowledge  which  has  thus  been  ac- 
quired by  astronomers  of  the  physical  characteristics  of 
the  sun  by  observation  with  the  telescope,  a  great  deal  of 


258  THE    SUN. 

information  has  been  obtained  within  a  few  years  in  re- 
spect to  its  chemical  composition  by  means  of  what  is 
called  the  spectrum  analysis.  A  few  words  must  be  said 
in  respect  to  this  subject,  though  it  is  not  very  directly, 
or,  at  least,  not  very  obviously  connected  with  the  subject 
of  this  volume. 

A  spectrum  is  a  colored  image  produced  by  the  separa- 
tion of  the  light  from  any  luminous  source  into  its  com- 
ponent colors  by  means  of  a  prism,  the  effect  of  the  prism 
being  to  refract  the  rays  in  different  degrees,  and  thus  to 
separate  them  from  each  other.  Now  the  light,  coming 
from  different  sources — as,  for  instance,  from  the  sun,  from 
a  star,  from  an  incandescent  metal,  from  the  electric  spark, 
from  the  combustion  of  iron,  or  hydrogen,  or  zinc  —  is 
found,  when  separated  in  this  manner  by  a  prism,  to  pro- 
duce spectra  very  different  in  appearance  from  each  other ; 
and  when  a  peculiar  apparatus  is  employed  that  is  con- 
structed with  great  delicacy  and  precision,  certain  lines  ap- 
pear— sometimes  dark,  sometimes  bright — crossing  it  in 
great  numbers  and  in  a  great  variety  of  positions  in  re- 
spect to  the  length  of  the  prism  and  to  each  other.  This 
subject  has  been  somewhat  more  fully  explained  in  the  vol- 
ume of  this  series  entitled  Light.  It  is  sufficient  for  our 
present  purpose  to  say  that  the  number,  character,  and  rel- 
ative position  of  these  lines  vary  according  to  the  nature 
of  the  incandescent  substance  which  emits  the  light,  its 
condition  of  aggregation — that  is,  whether  it  is  in  a  solid, 
liquid,  or  gaseous  state— and  the  character  of  the  media 
through  which  it  passes  in  coming  to  the  place  of  observa- 
tion. Many  thousand  of  these  lines  are  now  known,  and 
their  significance  understood.  To  the  uninitiated  observer, 
a  map  of  any  spectrum  would  exhibit  only  a  succession  of 
bands  of  bright  color  alternating  with  dark  lines,  forming 
a  combination  which,  though  exceedingly  beautiful,  would 


LANGUAGE    OF   THE    SPECTRUM.  259 

appear  hopelessly  complicated  and  unmeaning  to  a  person 
first  observing  them,  and  yet  to  the  spectroscopic  scholar 
every  portion  of  it  speaks  a  language  perfectly  precise  and 
clear.  To  him  every  bright  band  and  dark  line  has  a  mean- 
ing, depending  both  on  its  character  and  on  its  position, 
which  he  readily  and  perfectly  understands,  while  to  all 
others  it  seems  almost  inconceivable  that  there  can  be  any 
meaning  in  them,  just  as  it  would  seem  impossible  to  a 
savage,  when  shown  a  printed  book,  that  such  a  compli- 
cated and  interminable  aggregation  of  apparently  mean- 
ingless characters  could  possibly  be  the  vehicle  of  commu- 
nicating intelligence  of  any  kind  to  any  human  mind. 

And  it  is,  indeed,  a  great  study,  that  required  to  read 
and  understand  the  language  of  the  spectrum.  Many  men 
are  employing  themselves  almost  exclusively  in  these  in- 
vestigations. A  society  has  now,  at  the  time  of  this  writ- 
ing, been  formed  in  Italy  which  is  to  be  devoted  entirely 
to  the  work  of  perfecting  the  spectroscopic  apparatus  and 
pursuing  investigations  by  means  of  it,  especially  in  rela- 
tion to  the  constitution  of  the  sun,  and  they  have  com- 
menced the  publication  of  a  periodical  for  the  sole  purpose 
of  communicating  to  the  scientific  world  the  results  of  their 
investigations. 

The  results  that  have  been  attained  thus  far  show  con- 
clusively that  many  of  the  same  substances  that  go  to  com- 
pose the  mineral  strata  and  the  atmospheric  envelope  of 
the  earth  are  found  to  exist  in  the  sun,  and  also  in  many 
of  the  stars ;  and  that  the  same  laws  which  govern  the  ac- 
tion of  light  upon  this  planet  are  still  in  force  at  distances 
so  enormous  that,  while  light  moves  at  the  rate  of  192  mil- 
lions of  miles  in  a  second,  it  must  have  required,  in  some 
cases,  1000  years  to  traverse  the  distance  between  the  place 
of  its  emission  in  some  of  these  distant  orbs  to  the  spot 
where  it  enters  the  spectroscope  and  comes  under  the  ob- 


260  THE  SUN. 

servation  of  man.  What  a  proof  this  fact  affords  us  of  the 
vast  extent,  both  in  respect  to  space  and  duration,  over 
which  the  same  system  of  law  which  is  now  observed  to 
be  in  action  upon  this  earth  exercises  its  dominion  ! 

It  is  to  be  inferred  from  this  that  the  same  fundamental 
principles  in  respect  to  the  nature  and  the  action  offeree 
which  prevail  here  prevail  every  where,  and  that  the  solar 
force,  after  passing  through  all  the  changes  in  form  and 
character  which  we  see  exemplified  in  its  various  circuits 
over  the  earth,  continues  to  be  controlled  in  its  action,  aft- 
er it  is  radiated  away  from  the  earth  into  the  surrounding 
space,  by  the  same  laws  which  governed  it  while  subject 
to  our  observation  here.  We  can  not  follow  it  into  these 
regions,  nor  discover  the  mysterious  paths  by  which  it 
finds  its  way  back  at  last  to  the  source  from  which  it  flows 
to  us.  We  are  somewhat  in  the  situation  of  half-instruct- 
ed inquirers  into  the  philosophy  of  the  river's  flow.  They 
trace  the  stream  back  to  its  source  in  a  fountain  issuing 
from  the  ground,  which  seems  to  furnish  mysteriously  a 
never-ceasing  supply.  They  follow  it  in  its  downward 
course  till  it  is  lost  in  the  boundless  sea,  but  they  know 
nothing  of  the  wondrous  way  by  which  it  or  its  equivalent 
finds  its  way  back  through  invisible  evaporation,  and  drift- 
ing clouds,  and  falling  rain  on  the  mountain  tops,  and  infil- 
tration through  pervious  strata,  to  begin  its  course  through 
the  fountain  again.  They  have  glimpses,  it  is  true,  of  the 
clouds,  and  some  ideas  of  their  connection  with  evapora- 
tion from  the  sea,  and  with  the  fall  of  rain,  but  they  have 
not  yet  learned  to  connect  these  phenomena  together,  and 
to  see  them  as  parts  of  the  grand  system  provided  by  na- 
ture for  the  circulation  of  the  waters  of  the  globe. 

In  the  same  manner  we  trace  back  the  continuous  and 
unchanging  flow  of  force  which  we  see  passing  before  us 
to  its  unfailing  fountain  in  the  sun.  We  follow  it  on- 


VARIOUS    COSMICAL   PHENOMENA. 


261 


ward  in  the  same  way  through  all  its  circuitous  paths, 
through  the  air,  the  water,  and  the  organs  of  animal  and 
vegetable  life,  until  it  finally  passes  off  into  the  great  ocean 
of  space  around  us,  but  we  can  not  yet  see  by  what  means, 
or  through  what  paths,  it  or  its  equivalent  finds  its  way 
back  to  replenish  the  great  fountain  of  supply. 

We  have  glimpses,  it  is  true,  of  the  action  of  force  of 
some  kind  and  in  some  forms — in  the  meteors,  the  comets, 
the  auroral  and  zodiacal  light,  and  other  mysterious  celes- 
tial phenomena.  Meteors  are  seen  at  night,  and  even  by 
day,  shooting  through  the  sky ;  and  sometimes  they  seem 


THE   .MKTr.OK. 


262 


THE    SUN. 


to  enter  the  earth's  atmosphere,  where  they  are  heated  to 
incandescence  by  the  friction  of  the  air,  and  burst  with 
frightful  explosions,  throwing  down  large  fragments  to  the 
ground. 

The  zodiacal  light  is  a  luminous  track  or  space  seen  in 


THE  ZODIACAL  T.IGUT. 


MYSTERIES    UNSOLVED.  263 

certain  seasons  of  the  year,  following  the  sun  in  the  even- 
ing when  he  goes  down,  or  preceding  him  in  the  morning 
when  he  rises. 

There  have  been  various  surmises  as  to  the  cause  and 
the  nature  of  this  phenomenon,  but  there  is  little  known 
of  it  except  that  it  is  one  of  various  forms  in  which  the 
forces  existing  in  the  interstellar  spaces  are  embodied. 
We  have  not  yet  learned  to  interpret  the  significance  of 
these  various  phenomena,  still  less  to  connect  them  togeth- 
er, or  to  understand  what  part  they  bear  in  the  grand  sys- 
tem provided  by  nature  for  the  circulation  offeree  through- 
out the  universe — a  circulation  which  moves  on  in  a  per- 
petual flow  of  grandeur  and  majesty,  never  ending  and 
never  beginning. 


264  KICK   AGAIN. 


CHAPTER  XV. 

KICK   AGAIN. 

THERE  arc  various  avenues  through  which  the  knowl- 
edge of  external  realities  can  enter  the  mind.  When  any 
thing  is  told  us,  the  truth,  so  affirmed,  enters  through  the 
ear,  and  the  organs  connected  with  the  ear,  in  the  brain. 
When  we  read  it  in  a  book,  it  enters  through  the  eye. 
When  we  see  it  illustrated  in  a  diagram  or  in  a  pictorial 
representation,  it  enters  still  through  the  eye,  but  through 
a  different  set  of  organs  in  the  brain  from  those  which  take 
cognizance  of  the  signification  of  words.  Now,  when  a 
truth  enters  the  mind  by  any  two  of  these  or  other  ave- 
nues, even  if  it  is  not  apprehended  any  more  clearly,  it 
makes  a  much  stronger  and  more  lasting  impression  than 
when  it  enters  only  by  one. 

This  is  one  secret  of  the  great  efficiency  of  illustrations 
on  the  blackboard,  or  demonstrations  by  experiments. 
Many  persons  imagine  that  these  aids  are  mainly  useful  in 
conveying  a  clear  understanding  of  the  subject  to  the  pu- 
pil's mind.  But  in  many  cases  the  great  advantage  is,  not 
in  enabling  the  pupil  to  understand  the  subject  any  better, 
but  to  deepen,  and  strengthen,  and  make  more  permanent 
the  impression  which  the  truth  makes  upon  him. 

For  example,  to  take  a  very  simple  case,  if  in  a  school  of 
young  children  you  tell  them  that  when  a  four-sided  figure, 
with  square  corners,  has  all  its  four  sides  equal,  it  is  called 
a  square,  and  that  when  two  of  the  pairs  of  sides  are  lon- 
ger than  the  other  two,  so  as  to  make  it  longer  in  one  direc- 
tion than  it  is  in  the  other,  it  is  called  an  oblong,  they  may 


TWO   AVENUES   FOB  KNOWLEDGE.  265 

all  perfectly  understand  the  explanation,  but  the  impres- 
sion which  it  will  make  will  be  very  faint  and  evanescent. 
But  if  now  the  teacher  draws  the  figure  of  a  square,  and 
also  one  of  an  oblong  upon  the  blackboard,  and  writes  the 
name  of  each  in  a  legible  and  careful  manner  under  it,  so 
as  to  convey  to  the  children  the  same  truth  which  had  be- 
fore entered  by  words  through  the  ear,  now,  by  means  of 
vision  through  the  eye,  it  is  not  improbable  that  it  would 
make  an  impression  upon  them  so  strong  that  it  would 
never  be  effaced. 

It  is  not  so  much  the  superior  efficacy  of  one  of  these 
modes  over  the  other  upon  which  the  results  in  such  cases 
depends,  but  upon  the  conjoint  action  of  the  two.  For  if 
the  teacher  had  merely  drawn  the  two  figures,  with  the 
names  under  them,  upon  the  board,  and  had  then  only  ask- 
ed the  children  to  look  upon  them  long  enough  to  observe 
the  forms  and  to  read  the  names,  the  impression  would 
probably  have  been  as  faint  and  evanescent  as  before.  The 
visible  forms  must  be  accompanied  with  the  verbal  expla- 
nation to  secure  the  result. 

And  now  for  the  application  of  these  principles  to  our 
present  purpose.  These  truths  in  respect  to  the  origin  of 
almost  all  terrestrial  forces  in  the  agency  of  the  sun,  which 
have  been  presented  in  a  somewhat  methodical  and  con- 
nected manner  in  the  preceding  chapters,  had  been  explain- 
ed and  illustrated  in  a  much  more  simple  and  familiar  way 
by  Lawrence  to  John  and  Rick  Van  Dorn,  in  various  cas- 
ual conversations  that  he  held  with  them  in  their  walks 
or  fishing  excursions.  John  had  comprehended  the  sub- 
ject pretty  fully,  and  Rick  had  been  much  interested  in 
some  of  the  details  of  facts  which  Lawrence  presented  to 
his  mind  from  time  to  time,  though  he  had  not  made  much 
progress  in  comprehending  the  full  import  of  the  general 
principles  which  were  at  the  foundation  of  them.  So  Law- 
M 


266  KICK   AGAIN. 

rence  contrived  a  plan  to  present  somewhat  directly,  in  a 
visible  form,  the  general  truth  that  the  sun  stores  force  in 
plants  which  may  be  afterward  evoked  and  made  active 
by  man. 

Among  his  other  articles  of  apparatus  Lawrence  had  a 
small  toy  steam-engine,  which  was  intended  to  be  worked 
by  means  of  an  alcohol  lamp  placed  under  the  boiler.  He 
had  had  this  engine  for  some  time,  it  having  been  given  to 
him  when  he  was  quite  young.  Connected  with  this  he 
had  a  number  of  mechanical  toys,  some  of  which  he  had 
made  himself.  One  was  the  figure  of  a  man  sawing  wood, 
another  represented  a  shoe-maker  hammering  upon  his  lap- 
stone,  and  there  were  several  others.  These  were  connect- 
ed with  the  piston-rod  of  the  engine  in  such  a  manner  that 
the  engine,  when  in  operation,  set  them  all  at  work. 

Now  Lawrence  told  Rick  and  John  one  day  that  he  had 
a  plan  for  drawing  force  from  the  sun  to  work  his  little 
men,  though  he  told  them  it  would  take  some  time  to  gath- 
er enough  to  do  it.  In  saying  this,  he  took  some  peas  and 
beans,  and  planted  them  in  a  sunny  place  in  the  garden. 
Rick  looked  on  while  he  did  this,  somewhat  interested  it  is 
true,  but  much  puzzled.  He  did  not  see  at  all  what  con- 
nection there  could  be  between  planting  peas  and  beans, 
and  gathering  force  from  the  sun  to  keep  toy  carpenters 
and  shoe-makers  at  work. 

Lawrence  did  not  make  much  explanation  at  the  time 
when  the  planting  was  done,  but  simply  said,  when  the 
seed  was  in  the  ground, 

"  There  !  Now,  as  soon  as  they  come  up,  the  sun  will 
begin  to  lay  in  force  for  me — to  run  my  engine." 

So  they  all  went  away,  and  Rick  thought  no  more  of  the 
subject  for  two  or  three  wreeks.  At  length,  one  day,  when 
Rick  was  in  the  shop,  Lawrence  said,  "  Let  us  go  out  into 
the  garden,  and  see  how  my  store  of  force  is  going  on." 


STORED    FORCE    BROUGHT   INTO    USE.  267 

So  they  went  into  the  garden,  and  found  that  the  peas 
and  beans  were  up,  and  growing  quite  large. 

"  Yes,"  said  Lawrence,  "  every  thing  is  going  on  very 
well.  The  sun  is  storing  force  in  all  these  leaves  and 
stems." 

"  I  don't  see  any  force,"  said  Rick.  "  They  are  nothing 
but  common  peas  and  beans." 

"  And  yet  you'll  see  how  I  get  the  force  out  of  them  one 
of  these  days,"  said  Lawrence. 

The  next  time  that  Rick  came,  which  was  about  a  week 
afterward,  Lawrence  went  with  the  two  boys  into  the  gar- 
den again. 

"  Yes,"  said  he, "  the  experiment  has  gone  on  very  well. 
I  think  there  is  force  enough  gathered." 

So  he  cut  off  all  the  plants  close  to  the  ground,  and  car- 
ried the  vines  to  a  place  where  he  could  let  them  dry  in 
the  sun.  This  was  necessary,  for  if  he  had  evolved  the 
force  which  was  contained  in  the  tissues,  in  the  state  they 
were  then  in,  it  would  have  been  chiefly  absorbed  in  the 
work  of  evaporating  the  water  which  was  also  contained 
in  them,  and  the  vapor  which  would  thus  be  formed  he 
had  no  means  of  confining  so  as  to  make  it  work  his  engine. 
So  he  left  the  vines  to  be  dried  by  the  sun — that  is,  he  call- 
ed, as  it  were,  upon  the  sun  to  furnish  the  additional  force 
necessary  to  evaporate  the  water,  in  order  that  he  might 
have  the  use  of  all  that  was  stored  in  the  tissues  for  the 
work  which  he  wished  it  to  perform. 

At  length,  some  time  afterward,  when  the  vines  had  had 
time  to  become  thoroughly  dry,  he  made  a  somewhat  com- 
plicated arrangement  of  apparatus  for  bringing  this  latent 
force  into  action  in  a  manner  to  attract  Rick's  attention, 
and  fix  the  truth  which  he  was  attempting  to  elucidate  in 
his  mind.  He  took  a  gun-barrel,  which  he  kept  among 
his  apparatus  to  serve  the  purpose  of  an  iron  retort,  and, 


268  RICK    AGAIN. 

gathering  his  dry  vines  in  a  paper,  he  crowded  and  ram- 
med them  into  it  until  that  part  of  the  barrel  that  was  to 
go  into  the  fire  was  full. 

Then  he  connected  a  flexible  tube  at  one  end  with  a  cap 
which  fitted  over  the  muzzle  of  the  gun-barrel,  and  at  the 
other  end  with  a  small  metallic  pipe  which  he  fitted  in  the 
place  of  the  lamp  under  the  boiler.  By  this  arrangement, 
and  by  means  of  some  other  precautions  not  necessary  to 
be  described  here — since  this  book  is  not  intended  to  ex- 
plain the  details  of  chemical  manipulations — the  hydrogen 
gas,  brought  out  by  the  heat  from  the  dried  vines,  with  all 
the  stored  force  contained  in  it,  derived  from  its  forcible 
separation  from  oxygen,  and  its  prodigiously  strong  tend- 
ency to  reunite  with  it  so  soon  as  it  should  have  an  oppor- 
tunity, was  conveyed  under  the  boiler  of  the  little  steam- 
engine,  and  there  allowed  to  come  out  into  contact  with 
the  air,  and,  of  course,  with  the  oxygen  which  the  air  con- 
tained. 

Still  the  hydrogen,  notwithstanding  this  very  strong 
tendency  to  unite  with  oxygen,  for  some  mysterious  reason 
can  not  do  so  while  both  are  cool.  While  the  hydrogen 
was  in  the  gun-barrel,  although  it  was  very  hot  there,  it 
did  not  combine  with  oxygen,  for  there  was  none  there. 
All  oxygen  was,  of  course,  entirely  excluded  from  the  in- 
terior of  the  barrel.  And  when  the  hydrogen  issued  from 
the  pipe,  and  so  came  into  contact  with  the  oxygen  of  the 
outer  air,  it  could  not  even  then  begin  to  combine,  because 
it  was  not  now  any  longer  hot,  having  become  cooled  in 
passing  through  the  tube.  But  if  ever  so  small  a  portion 
of  it  could  be  heated  to  the  right  point,  when  it  was  in  con- 
tact with  the  oxygen,  the  two  would  immediately  combine 
with  great  force,  and  this  force  would  appear  in  the  form 
of  heat,  which  would  immediately  act,  too,  in  raising  the 
portions  of  the  gases  next  to  it  to  the  right  temperature, 


SUCCESSFUL   RESULT.  269 

and  so  the  union  would  continue  to  go  on  with  great  ener- 
gy as  fast  as  the  hydrogen  issued  from  the  mouth  of  the 

pipe- 
Such  is  the  philosophy  of  the  burning  of  gas  issuing 
from  a  tube. 

The  energy,  in  the  form  of  heat,  which  is  furnished  by 
the  reunion  of  the  oxygen  and  hydrogen,  separated  previ- 
ously by  the  action  of  the  sun,  is  far  greater  than  is  neces- 
sary for  carrying  on  the  process  of  combustion.  In  the 
case  of  Lawrence's  experiment,  a  great  portion  of  the  heat 
— that  is,  of  the  force  in  that  form — passed  up  through  the 
bottom  of  the  boiler,  and  transferred  itself  to  the  water, 
converting  it  into  steam.  The  steam,  in  its  turn,  deliver- 
ed the  force  to  the  piston  in  the  little  cylinder,  and  this 
communicated  it  to  the  piston-rod,  and  this  to  the  wheels 
and  bands  connected  with  the  mechanism  of  the  figures, 
and  in  a  very  short  time  all  the  little  men  were  as  busy  at 
their  work  as  if  they  had  been  alive. 

"  There !"  said  Lawrence,  as  his  experiment  arrived  at 
this  successful  result ;  "  see  how  I  make  the  men  work  by 
the  force  I  gathered  from  the  sun  by  means  of  my  peas  and 
beans." 

"It  is  not  the  peas  and  beans  at  all,"  said  Rick;  "it  is 
your  steam-engine." 

"  But  where  does  the  force  come  from  to  make  the  en- 
gine work?" 

"  It  don't  come  from  any  where,"  said  Rick.  "  All  you 
have  to  do  is  to  make  a  fire  under  the  boiler.  That's  the 
way  with  all  steam-engines." 

Thus  it  appeared  that,  after  all,  Rick  had  not  very  clear- 
ly comprehended  the  principles  which  this  experiment  was 
intended  to  illustrate.  But  the  lesson  was  not  lost  upon 
him  by  any  means.  The  visible  embodiment  of  the  prin- 
ciple which  the  experiment  presented  to  him  remained  pic- 


270  KICK   AGAIN. 

tured  in  his  imagination  for  years.  It  gave  him  a  glimpse 
of  the  truth  at  the  time,  and  the  memory  of  it  aided  him 
greatly  in  perceiving  the  full  force  and  extent  of  it  long 
years  afterward. 

It  happened  very  frequently,  in  the  various  interviews 
which  took  place  between  Lawrence,  John,  and  Rick,  and 
in  the  conversations  which  Lawrence  held  with  the  two 
boys,  that  Rick  very  imperfectly  comprehended  what  Law- 
rence explained,  while  John,  whose  mind  was  more  mature 
in  respect  to  the  reception  of  general  truths,  understood 
them  much  more  fully.  For  example,  one  day,  when  the 
thi'ee  were  returning  from  an  excursion  which  they  had 
been  making  together,  they  came  to  a  place  where  an  old 
man  and  his  grandson  were  at  work  making  hay.  The  old 
man  had  proposed  that  morning,  at  dinner,  that  he  and  Jo- 
sie  should  go  down  and  work  a  little  upon  the  hay  that 
afternoon. 

"  We  can  not  do  much,"  said  he  to  himself, "  for  he  is  too 
young,  and  I  am  too  old.  But  we  can  do  something ;  and 
after  every  half  hour  of  work  we  will  take  a  little  time  for 
rest." 

Just  as  Lawrence  and  his  party  came  along,  the  two 
hay-makers  had  come  to  a  recess,  as  Josie  called  it,  and  had 
just  gone  to  sit  down  upon  a  log,  near  the  field,  to  rest. 

Now  Lawrence  had  been  explaining  to  Rick  and  John 
that  very  afternoon  that  all  the  strength  that  we  exercise 
in  the  action  of  all  our  bodily  organs,  whether  of  the  limbs 
or  of  the  brain,  is  derived  from  the  stored  force  laid  up  in 
the  food  which  we  take,  and  this  force  tends  to  expend  it- 
self in  young  animals  through  the  organs  of  motion,  lead- 
ing them  to  take  pleasure  in  all  kinds  of  rapid  bodily  move- 
ment, while  in  the  old  a  larger  portion  of  it  comes  into  ac- 
tion through  the  organs  communicating  more  immediate- 
ly with  the  mind.  Now  he  and  the  two  boys  came  by  the 


FUNNY    RESTING.  273 

place  where  the  hay-makers  had  been  working  just  at  the 
time  when  the  old  man  and  Josie  had  gone  to  take  their 
seat  on  the  log. 

Josie  had  asked  his  grandfather,  just  before  they  had  sat 
down,  whether  it  was  not  time  for  them  to  take  a  rest,  for 
he  said  he  was  so  tired  he  could  not  possibly  do  any  more ; 
and  so  they  had  sat  down  together  on  the  log.  But  they 
had  not  been  there  more  than  two  minutes  before  Josie, 
having  recovered  his  breath  a  little,  jumped  up  and  began 
to  climb  the  gnarled  and  misshapen  old  oak,  under  the 
shadow  of  which  the  log  which  his  grandfather  had  taken 
for  a  seat  was  lying.  His  grandfather  had  remonstrated 
at  first,  asking  him  why  he  wanted  to  climb  that  tree.  It 
would  be  a  great  deal  better,  he  said,  for  him  to  sit  still 
and  rest.  But  Josie  said  that  he  was  rested  already,  and 
so  went  on  climbing.  It  was  when  he  had  reached  a  con- 
siderable height  upon  this  tree  that  Lawrence  and  the  two 
boys  came  along  by  a  path  on  the  other  side  of  it. 

"  Hi-yo !  Josie,"  said  Rick,  calling  out  to  him, "  what  are 
you  doing  there  ?" 

""We're  resting,"  said  Josie.  "Grandfather  and  I  have 
been  making  hay,  and  we're  resting." 

The  truth  is,  that  the  supply  offeree  introduced  into  the 
system  in  the  food,  while  it  must  always  reappear  in  some 
way,  makes  itself  manifest  in  very  different  forms  in  the 
same  system,  and  the  proportions  in  which  it  appears  in 
these  different  forms  vary  very  much  at  different  periods 
of  life.  A  portion  of  it  develops  itself  as  heat,  and  is  em- 
ployed in  keeping  the  body  warm.  Another  portion  is  ex- 
pended in  giving  strength  to  the  muscles  and  limbs,  and 
another  still  in  maintaining  the  action  of  the  vital  organs, 
and  even,  as  is  now  generally  believed,  those  of  the  brain, 
through  the  instrumentality  of  which,  in  some  mysterious 
way,  the  mind  performs  its  functions.  In  childhood  and 
M2 


274  KICK  AGAIN. 

youth  the  force  expends  itself,  in  most  of  these  ways  in  a 
rapid  and  fitful  manner,  changing  from  one  to  another  in- 
cessantly, the  different  limbs  and  organs  becoming  easily 
fatigued,  and  also  being  very  soon  and  very  easily  restored 
by  a  brief  period  of  repose.  In  age  the  action  in  all  these 
modes  is  more  steady  and  slow,  and  the  change  from  one 
form  of  expenditure  to  another  is  much  less  frequently  de- 
manded. 

So  Josie,  in  the  case  referred  to,  had  not  remained  five 
minutes  upon  the  log  before  he  felt  rested,  and  the  force 
within  him  had  begun  to  accumulate  and  to  demand  fresh 
outlets  through  which  to  expend  itself.  It  found  these 
outlets  in  the  exercise  of  his  limbs  in  climbing  the  tree,  and 
in  those  movements  in  his  brain  that  wrere  concerned  in  the 
curiosity  which  he  felt  in  seeing  whether  there  was  a  bird's 
nest  or  a  squirrel's  nest  among  the  branches,  or  in  the  ex- 
citement and  pleasure  which  the  strange  appearance  of  ev- 
ery thing  beneath  and  around  him  would  assume  when 
viewed  from  his  lofty  position.  In  the  mean  time  Law- 
rence and  the  two  boys  came  to  the  place,  and  Lawrence, 
being  acquainted  with  the  old  man,  took  a  seat  beside  him 
on  the  log  and  began  to  talk  with  him  about  old  times, 
and  the  old  man  soon  became  greatly  interested  in  recall- 
ing and  relating  the  incidents  of  his  early  youth,  when  all 
that  part  of  the  country  was  in  so  different  a  condition. 

Josie  soon  came  down  from  the  tree,  and  stood  for  a  mo- 
ment listening  to  the  conversation  between  Lawrence  and 
his  grandfather,  but  very  soon  he  and  Rick  set  off  to  run 
down  toward  a  little  brook  which  flowed  near,  and  where, 
he  said,  he  thought  there  were  some  fishes.  Josie  went 
dancing  and  capering  backward  along  the  path  before  Rick 
as  if  he  had  not  done  any  work  for  a  week. 

John  preferred  to  stay  under  the  tree,  and  very  soon  he 
took  a  seat  upon  the  log  by  the  side  of  Lawrence.  He  sat 


EVOLUTION  OP  FORCE  FROM  FOOD.         275 

there  for  a  long  time  listening  with  Lawrence  to  the  old 
man's  stories. 

When  afterward,  in  continuing  their  walk,  Lawrence  ex- 
plained to  the  boys  that  the  force  which  sustained  all  the 
activity  that  they  had  observed  in  the  two  cases — that  of 
the  mind  in  the  man,  and  of  bodily  motion  in  the  boy — 
was  derived  from  the  effect  of  the  food  which  they  had 
taken,  in  bringing  with  it  into  their  systems  force  stored 
in  it  by  the  sun,  Rick  said  that,  in  respect  to  Josie,  he  did 
not  believe  it  was  any  thing  that  he  ate  that  made  him  act 
so,  but  only  his  love  of  fun  ! 


276  DETONATIONS  AND   EXPLOSIONS. 


CHAPTER  XVI. 

DETONATIONS   AND   EXPLOSIONS. 

WHEN  a  certain  degree  offeree  is  very  suddenly  set  free, 
there  is  often  produced  what  we  call  a  detonation  or  an 
explosion,  using  the  one  term  or  the  other  according  to 
the  quantity  of  force  which  is  brought  into  action. 

Thus  the  quantity  of  force  produced  by  the  sudden  com- 
bustion or  other  chemical  action  taking  place  in  the  com- 
position contained  in  a  boy's  torpedo,  when  thrown  upon 
the  pavement,  is  small,  and  we  call  the  result  a  detonation. 
In  the  case  of  the  powerful  torpedoes  inclosed  in  iron  cases, 
and  used  for  blowing 'up  hostile  ships  at  the  entrance  to  a 
harbor,  a  precisely  similar  effect,  and  one  produced,  too,  by 
similar  means,  though  vastly  more  powerful,  is  called  an 
explosion.  The  noise  that  is  produced  both  by  detonations 
and  explosions  is  due  altogether  to  the  action  of  the  liber- 
ated force  upon  the  air.  The  sudden  heat  that  is  developed 
expands  and  drives  back  the  air  in  all  directions,  and  the 
sudden  return  of  it  produces  a  shock  attended  with  a  vari- 
ety of  concussions  which  sends  abroad  in  every  direction 
through  the  surrounding  atmosphere  that  kind  of  confused 
medley  of  vibrations  which  in  their  effect  upon  the  ear 
constitute  what  we  call  noise.  If  there  were  no  air,  the 
most  tremendous  explosion  that  can  be  conceived  would 
produce  no  sound. 

The  most  rapid  mode  by  which  force  can  be  developed — 
that  is,  brought  out  from  a  latent  into  an  active  state — is 
by  some  kind  of  chemical  action,  usually  combustion,  which 


EXPLOSIVE   SUBSTANCES.  277 

word,  in  fact,  only  denotes  that  kind  and  degree  of  chem- 
ical action  which  is  so  rapid  as  to  be  attended  with  the 
evolution  of  light  and  heat ;  but,  even  by  this  means,  the 
force  would  not  be  ordinarily  evolved  with  the  degree  of 
rapidity  necessary  to  produce  an  explosion  without  anoth- 
er condition  which  will  be  hereafter  explained. 

The  most  effective  substances  in  ordinary  use  to  produce 
explosive  force  are  gunpowder,  gun-cotton,  nitro-glycerine, 
dynamite,  and  the  like,  all  of  which  act  on  substantially 
the  same  principle,  namely,  that  of  producing  an  extremely 
rapid  combustion  by  bringing  large  quantities  of  oxygen 
on  the  one  hand,  and  of  carbon  and  hydrogen  on  the  other, 
into  close  juxtaposition  with  each  other,  so  that  they  may 
rapidly  combine. 

For  one  of  the  great  fundamental  facts  in  the  economy 
of  nature,  as  we  observe  it,  is  this :  that  far  the  greater 
portion  of  the  action  which  we  see  taking  place  around  us 
on  this  globe  consists  in  the  energy  put  forth  by  the  sun 
in  separating  carbon  and  hydrogen  from  oxygen,  and  then, 
as  the  counterpart  and  correlative  of  this,  the  intense  ea- 
gerness manifested  between  the  oxygen,  and  the  carbon, 
and  hydrogen  in  coming  together  again. 

Now  the  whole  philosophy  of  the  explosive  force  mani- 
fested by  gunpowder  and  the  other  substances  above 
named  consists  in  their  composition  being  such  as  to  bring 
quantities  of  carbon  and  hydrogen  on  the  one  hand,  and  of 
oxygen  on  the  other,  into  close  juxtaposition,  so  that  they 
may  unite,  and  thus  liberate  and  restore,  as  it  were,  the 
force  that  was  expended  in  separating  them,  with  the. 
greatest  rapidity. 

To  illustrate  this,  suppose  we  have  a  large  and  solid  log 
of  dry  wood.  Now  the  wood  of  such  a  log  contains  carbon 
and  hydrogen,  but  no  oxygen.  The  oxygen  is  in  the  air 
around  it.  When  the  substances  are  raised  to  the  right 


278  DETONATIONS   AND   EXPLOSIONS. 

temperature  to  bring  their  tendency  to  combine  into  action, 
the  log  begins  to  bui'n — that  is,  the  oxygen  combines  with 
all  that  portion  of  the  carbon  and  hydrogen  which  lies  on 
the  surface  of  the  log,  which  is  all  that  is  accessible  to  it  at 
first;  and  it  can  only  gain  access  to  the  inner  portions  as 
fast  as  the  outer  ones  are  burned  away. 

If  now  the  log  is  split  up  into  small  and  slender  portions, 
and,  still  more,  if  it  is  converted  into  shavings  by  a  plane, 
the  air — that  is  to  say,  the  oxygen  that  is  in  it — gains  a 
much  more  ready  access  to  the  substance  of  the  wood,  be- 
ing able  to  introduce  itself  into  the  interstices  of  the  heap 
of  sticks  or  shavings,  and  the  combustion  will  be  greatly 
accelerated ;  and,  ponsequently,  the  force  that  is  developed, 
though  it  will  be  no  greater  in  the  total  amount,  will  come 
forth  from  its  latent  into  an  active  state  in  a  much  more 
rapid  manner. 

And  if  it  were  possible  to  reduce  the  wood  to  dust  by  a 
rasp  or  a  saw,  and  then  to  keep  the  particles  suspended  in 
the  air,  and  near  enough  to  each  other  to  furnish  to  each 
portion  of  carbon  and  hydrogen  a  portion  of  oxygen,  nei- 
ther more  nor  less  than  it  required,  close  at  hand,  the  whole 
mass  would  flash,  as  it  were,  into  a  flame  with  almost  the 
suddenness  of  gunpowder. 

Indeed,  the  dust  of  wood  or  of  coal  mingled  thus  with 
air  is  sometimes  blown  into  furnaces,  and  is  found  to  pro- 
duce a  wonderful  effect,  through  the  rapidity  and  the  force 
of  the  combustion  which  results. 

Now  the  oxygen  in  the  air,  being  a  gas,  can  not  be  kept 
mingled  in  this  way  with  any  powdered  substance.  If  it 
could  be  obtained  in  a  solid  form,  and  could  be  pulverized, 
and  in  that  form  mingled  intimately  with  any  powdered 
compound  of  carbon  and  hydrogen,  then,  when  a  portion 
of  the  mass  was  raised  to  the  right  temperature,  an  almost 
instantaneous  combination,  accompanied  with  a  sudden  de- 


NATURE   OP  NITROGEN.  279 

velopment  of  force  in  the  form  of  heat,  and  having  the  ef- 
fect of  an  explosion,  would  result. 

But  oxygen  can  not  be  made  to  exist  by  any  means  now 
known  in  a  solid  form,  except  in  combination  with  some  oth- 
er substance.  The  best,  therefore,  that  can  be  done  is  to 
use  it  in  combination  with  some  other  substance  for  which 
it  lias  the  weakest  possible  affinity — that  is,  the  one  which 
will  most  easily  and  readily  let  go  its  hold,  so  as  to  allow 
the  oxygen,  with  the  least  hinderance,  to  enter  into  combi- 
nations with  the  hydrogen  and  carbon.  This  substance  is 
nitrogen. 

The  great  distinguishing  characteristic  of  nitrogen  is 
the  weakness  of  its  affinity  for  other  substances,  just  as 
the  strength  of  its  affinity  is  the  great  characteristic  of  ox- 
ygen. Now  nitrogen  will  combine  with  oxygen  in  various 
ways  and  in  many  different  proportions,  the  two  elements 
being  at  all  times  ready  to  let  go  at  once  their  hold  upon 
each  other  whenever  any  other  substance  is  presented  for 
which  oxygen  has  a  stronger  attraction. 

Nitrogen  is  usually  described  in  books  as  one  of  the 
most  inert  substances  in  nature,  and  yet  the  compounds 
which  it  forms  with  other  elements,  and  especially  with 
oxygen,  are  the  most  violent  in  their  action  of  all  known 
substances.  Nitric  acid  is  perhaps  the  principal  of  these 
combinations,  and  is  one  of  the  most  powerful  and  destruct- 
ive agents  that  exist.  It  consists  essentially  of  a  large 
quantity  of  oxygen  held  in  combination  with  a  smaller 
quantity  of  nitrogen,  united  to  it  by  a  very  feeble  force. 
People  are  often  surprised  that  a  substance  so  inert  should 
form  compounds  so  active  and  violent ;  but,  instead  of  its 
being  a  matter  of  surprise  that  this  should  be  the  case,  it 
is  the  very  inertness  of  this  element  on  which  the  violence 
of  the  action  of  the  compound  depends — that  is,  it  holds 
the  oxygen  committed  to  its  keeping  with  so  feeble  a  grasp, 


280  DETONATIONS    AND   EXPLOSIONS. 

and  releases  it  so  readily,  that  this  last  immensely  power- 
ful agent  is  always  at  once  set  free,  and  enabled  to  act  with 
its  full  force  upon  other  substances.  It  is  the  oxygen 
which  is  really  the  agent  in  all  the  violent  action  which 
results,  the  nitrogen  only  serving  the  purpose  of  holding  it 
weakly,  and  releasing  it  readily,  when  the  time  for  action 
comes. 

Still,  however  rapidly  the  process  of  combustion  may  be 
made  to  proceed  by  this  arrangement— in  the  case,  for  ex- 
ample, of  gunpowder — the  force  is  not  developed  with  suf- 
ficient suddenness  and  in  sufficient  quantity  to  produce  all 
the  effects  of  an  explosion  without  being  restrained  and 
allowed  to  accumulate  its  energy.  Thus  an  ounce  of  gun- 
powder, ignited  in  the  open  air,  burns  with  a  flash  indeed, 
but  the  combustion  of  it  requires  a  perceptible  period  of 
time,  and  the  force  developed  has  time  to  pass  off  into  the 
air  without  any  very  sudden  or  violent  action;  but  let 
the  same  quantity  be  inclosed  in  the  cast-iron  shell  of  a 
hand-grenade,  or  rammed  into  a  gun-barrel,  or  into  a  hole 
drilled  into  a  rock,  and  confined  there  with  wadding  or 
tamping,  so  that  the  force  which  results  from  the  begin- 
ning of  the  burning,  can  be  held  in  restraint  until  the  com- 
bustion is  completed,  then,  when  it  at  last  breaks  away, 
and  the  whole  accumulated  force  comes  into  action  in  a 
single  instant,  a  very  violent  explosion  is  the  result. 

There  are  many  other  ways  in  which  force,  developed 
gradually,  may  be  accumulated  and  allowed  to  act  all  at 
once  so  as  to  produce  an  explosion.  The  bursting  of  a 
steam-boiler  is  one  example  of  this,  and  the  accumulation 
of  some  mysterious  force  in  the  case  of  a  volcano,  until  it 
acquires  energy  sufficient  to  burst  the  barriers  that  confine 
it,  is  another. 

In  the  case  of  the  steam-engine,  the  force  gradually  pro- 
duced by  the  heat  from  the  coal,  acting  upon  the  steam, 


MEASOTIINO  THE   BURSTING  PEKBSX7EE. 


EXPERIMENTS    ON   PRESSURE.  283 

works  itself  off,  when  all  is  right,  through  the  machinery ; 
or,  if  there  is  any  tendency  to  accumulation,  the  safety 
valve  allows  the  surplus  to  escape.  When,  from  any  cause, 
the  force  accumulates  too  rapidly  to  pass  off  through  these 
avenues,  it  increases  in  tension  until  it  becomes  sufficient  to 
overcome  the  cohesive  strength  of  the  iron  of  the  boiler, 
and  an  explosion  is  the  result. 

The  precise  degree  of  this  tension  may  be  exactly  meas- 
ured. It  is  obviously  of  the  nature  of  a,  pressure,  and  it  is 
measured  and  estimated  sometimes  by  the  number  of 
pounds  to  the  square  inch,  and  sometimes  by  what  are  call- 
ed atmosphere*.  The  pressure  of  the  atmosphere  is  about 
fifteen  pounds  to  the  square  inch,  so  that  a  pressure  of  two, 
three,  or  ten  atmospheres  would  be  that  of  thirty,  forty- 
five,  or  one  hundred  and  fifty  pounds  to  the  square  inch 
respectively.  In  locomotive  engines,  the  pressure  employ- 
ed is  often  from  fifty  to  sixty  pounds  to  the  square  inch. 

Great  as  the  pressure  is,  in  many  cases,  which  acts  upon 
the  interior  surface  of  a  large  boiler,  it  can  be  conveyed 
very  easily,  by  small  pipes,  to  a  great  distance,  and  there 
observed  and  measured  safely.  In  this  way  some  experi- 
ments were  made  during  the  last  year,  under  the  direction 
of  the  Navy  Department  of  the  United  States,  to  ascertain 
certain  points  in  respect  to  the  amount  of  pressure  realized 
in  large  boilers  when  raised  to  the  bursting  point.  The 
experiments  were  made  upon  Sandy  Hook,  at  a  place  far 
removed  from  any  dwelling.  The  engraving  shows  the  ef- 
fect produced  by  one  of  the  explosions. 

In  the  middle  distance  is  seen  the  inclosure  where  the 
boilers  to  be  experimented  upon  were  stored,  and  a  repre- 
sentation of  the  result  of  one  of  the  explosions.  In  the 
foreground  is  also  the  place  where  the  observers  were  sta- 
tioned. Pipes  are  seen  lying  upon  the  ground,  and  form- 
ing a  communication  between  the  boiler  experimented 


284  DETONATIONS   AND   EXPLOSIONS. 

upon  and  the  station.  These,  being  connected  with  the 
boiler  at  one  end,  and  with  the  gauges  at  the  station  at  the 
other  end,  afford  the  means  of  determining  the  pressure  in 
the  boiler  at  each  different  stage  of  the  experiment.  There 
were  several  boilers  tested.  In  one  of  them,  when  the 
pressure  reached  fifty  pounds  to  the  inch,  one  of  the  interi- 
or braces  gave  way ;  and  when,  at  length,  the  index  of  the 
gauge  marked  fifty-three  pounds  to  the  inch,  the  boiler 
burst  with  a  terrific  explosion,  and  portions  of  it,  and  of 
the  shell  connected  with  it,  weighing  about  four  tons,  were 
hurled  high  into  the  air,  and  thrown  to  a  distance  of  500 
feet  from  the  inclosure. 

The  great  violence  of  the  effect,  in  cases  like  this,  where 
force  is  held  in  restraint  for  a  time  after  being  brought  into 
great  tensile  action,  arises  from  its  being  converted  into  heat 
by  the  compression,  the  prevention  of  motion  seeming  to 
operate  in  some  sense  in  the  same  way  as  the  extinguish- 
ment of  it.  In  the  case  of  gunpowder,  the  gases  produced 
by  the  combustion,  of  the  carbon  and  sulphur,  by  means  of 
the  oxygen  in  the  nitre,  are  found  to  occupy  about  500 
times  the  space  occupied  by  the  gunpowder  itself.  This 
is  an  enormous  expansion ;  but  if  this  expansion  is  pre- 
vented for  a  moment  from  taking  effect  by  the  resistance 
of  the  sides  of  the  gun-barrel,  or  of  rock,  within  which  the 
combustion  goes  on,  the  gases  become  heated  so  as  to  de- 
mand 2500  times  the  original  space ;  and  this  is  the  cause 
of  the  enormous  increase  in  the  violence  of  the  effect  pro- 
duced by  the  combustion  of  such  substances  when  it  takes 
place  under  confinement.  With  some  of  the  immense  guns 
now  manufactured  by  the  English  and  American  govern- 
ments, balls  weighing  500  pounds  are  thrown  with  such 
force  as  completely  to  penetrate  a  target  consisting  of  a 
plate  of  solid  iron  eight  inches  thick,  backed  by  six  inches 
of  the  very  hardest  kind  of  wood,  behind  which  is  another 


THE    EFFECT   HOW   PRODUCED.  285 

plate  of  iron  Jive  inches  thick,  with  another  thickness  of  six 
inches  of  hard  wood  beyond  it,  and  a  one  and  a  half  inch 
plate  of  iron  in  the  rear — the  whole  all  firmly  riveted  to- 
gether ! 

Besides  gunpowder,  there  are  various  other  explosive 
substances,  such  as  gun-cotton,  nitro-glycerine,  dynamite, 
and  others,  the  properties  of  which  depend  upon  a  consti- 
tution substantially  the  same  in  principle  with  that  of  gun- 
powder, namely,  the  combining  of  a  substance  consisting 
chiefly  of  carbon  and  hydrogen  with  some  other  substance 
containing  a  large  quantity  of  oxygen  in  a  state  of  conceal- 
ment or  disguise,  as  it  were.  In  gunpowder,  the  combusti- 
ble substances — the  sulphur  and  carbon — are  finely  pulver- 
ized in  a  mill,  as  is  also  the  nitre  which  contains  the  oxygen. 
In  gun-cotton,  on  the  other  hand,  nature  divides  the  com- 
bustible material  by  forming  the  long,  slender  filaments  of 
the  cotton,  and  the  oxygen  is  added  by  means  of  a  combi- 
nation of  acids  containing  it,  which  infiltrates  itself  into 
the  substance  of  the  fibre,  and  thus  brings  the  two  ele- 
ments into  a  much  closer  connection  with  each  other  than 
can  possibly  be  effected  by  any  mere  mechanical  means. 
It  is  substantially  the  same  with  nitro-glycerine,  and  with 
a  composition  called  dualin,  which  are  estimated  to  exert 
by  their  combustion  ten  times  the  force  of  gunpowder ! 

These,  and  perhaps  most  other  explosive  substances  now 
used,  depend  for  their  effect  on  the  very  energetic  manner 
in  which  oxygen,  when  held  weakly  by  nitrogen,  under 
certain  conditions  lets  go  its  hold  and  seizes  upon  any  car- 
bon or  hydrogen  that  is  within  its  reach.  And  not  only 
these,  but  a  great  many  of  the  most  remarkable  phenomena 
of  nature  depend  upon  this  relation  which  the  action  of  ni- 
trogen and  that  of  oxygen  have  to  each  other.  The  read- 
er should  bear  this  principle  distinctly  in  mind,  namely, 

That  the  counterpart  of  oxygen  in  the  economy  of  nature, 


286  DETONATIONS   AND   EXPLOSIONS. 

in  respect  to  the  strength  of  affinity  for  other  substances, 
and  its  tenacity  of  hold  when  in  combination  with  them, 
is  nitrogen.  Nitrogen  is  the  great  weak-holder.  It  is  as 
remarkable  for  the  feebleness  of  its  tendency  to  unite  with 
other  substances,  and  the  readiness  with  which  it  gives 
them  up  to  other  affinities,  as  oxygen  is  for  the  contrary 
qualities. 

And  a  very  large  proportion  of  the  processes  going  on 
all  the  time  in  the  natural  world,  and  of  the  phenomena  of 
animal  and  vegetable  life,  are  dependent  upon  the  mutual 
play  and  interaction  of  these  two  elements  in  relation  to 
themselves  and  to  other  substances,  as  determined  by  the 
weak  affinities  of  the  one,  and  the  strong  affinities  of  the 
other. 

Thus,  as  we  saw  in  the  preceding  chapter,  the  forcible 
separation  of  oxygen  from  its  strong  combinations,  by  the 
power  of  the  sun,  in  the  leaves  of  plants,  and  the  delivery 
of  it  to  the  weak  custody  of  nitrogen,  and,  finally,  the  sur- 
rendering of  it  back,  under  new  circumstances,  to  its  strong 
combinations  again,  is  the  secret  of  a  very  large  portion 
of  the  phenomena  of  vegetable  and  animal  life.  It  is  in  ac- 
cordance with  this  view  that  plants  have  comparatively 
little  need  of  air,  and  that  chiefly  for  the  sake  of  the  carbon 
which  the  air  contains ;  but  animals  have  great  need  of  it, 
on  account  of  the  oxygen  which  they  use  for  the  sake  of 
the  heat-force  which  they  obtain  by  letting  it  fall  into 
combination  with  the  carbon  again. 

Some  persons  are,  at  first  thought,  surprised  that,  since 
this  is  the  state  of  the  case — that  is,  since  oxygen  has  so 
strong  an  affinity  for  other  substances,  and  as  so  large  a 
quantity  of  it  is  held  in  the  air,  and  in  a  peculiarly  weak 
union  with  nitrogen — for  the  air  is  chiefly  composed  of 
those  two  elements — that  the  action  of  the  air  is  not  more 
instantaneous  and  violent  than  it  is.  The  explanation  is, 


OTHER   VIOLENT   CHEMICAL   ACTION.  287 

that  the  oxygen  in  the  air  can  not  act  with  very  great  ra- 
pidity or  energy  on  account  of  the  wide  diffusion  and  ex- 
treme dilution  of  it.  The  proportion  in  the  atmosphere  is 
only  about  one  quarter  of  its  bulk,  and  the  substance  of  it 
is  so  minutely  divided  and  so  much  diffused  that  the  in- 
tensity of  its  action  is  greatly  diminished  in  consequence 
of  the  limited  supply  of  it  which  any  given  current  of  air 
can  bring  into  action  in  any  given  time. 

There  are  many  other  examples  of  chemical  action  so  en- 
ergetic as  to  produce  detonations  and  explosions,  the  ef- 
fect of  which  is  dependent  upon  the  powerful  attraction  of 
certain  other  substances  possessing  in  some  degree  the 
characteristics  of  oxygen.  There  are  also  certain  metals 
that  have  so  ardent  an  affinity  for  oxygen  that  they  seize 
it  with  even  greater  avidity  than  that  which  is  manifested 
by  the  action  of  carbon  or  hydrogen  upon  it.  They  seize 
it  wherever  they  find  it,  no  matter  how  strong  its  existing 
combination  may  be.  Two  very  conspicuous  examples  of 
these  are  the  metals  potassium  and  sodium — the  bases  re- 
spectively of  potash  and  soda.  These  metals  have  so  ex- 
cessively strong  an  affinity  for  oxygen  that  they  decom- 
pose water  to  obtain  it ;  and  they  can  not  be  retained  in  a 
metallic  state  without  very  special  and  effectual  precau- 
tions to  protect  it  from  the  water  existing  in  the  atmos- 
phere, and  in  almost  all  substances  around  them. 

And  the  action,  moreover,  is  so  violent  that  all  the  phe- 
nomena of  combustion  are  produced  when  they  are  brought 
into  contact  with  water.  It  is  very  wonderful  to  see  a 
globule  of  either  of  these  metals  burst  into  a  blaze  when 
thrown  into  water,  or  placed  on  a  wet  surface  of  any  kind. 

The  great  heat  developed  by  this  intense  action  is  made 
use  of  to  produce  explosive  effects  by  arranging  the  ma- 
terials in  such  a  way  as  to  allow  them  suddenly  to  com- 
bine in  any  confined  space.  This  has  been  tried  especially 


288  DETONATIONS   AND   EXPLOSIONS. 

with  sodium,  by  inclosing  a  portion  of  it,  and  also  a  por- 
tion of  water,  in  two  glass  tubes  connected  together  by  a 
narrow  neck  or  division,  somewhat  like  that  of  an  hour- 
glass. This  neck  is  closed  by  a  division  formed  of  some 
substance  soluble  in  water,  such  as  sugar,  or  salt,  or  a  film 
of  gum,  or  glue.  The  charge,  thus  prepared,  is  placed,  for 
example,  in  the  hole  drilled  in  a  rock,  and  closely  confined 
there  by  a  wadding  or  tamping  rammed  in.  After  the 
lapse  of  a  certain  time,  which  can  be  calculated  with  some 
accuracy  beforehand,  the  dividing  substance  is  dissolved 
by  the  water  which  is  in  contact  with  it  on  one  side,  and 
the  water  and  the  sodium  rush  together.  The  water  is  de- 
composed. The  oxygen  of  it  combines  with  the  sodium 
and  forms  soda.  The  other  element  of  the  water — that  is, 
the  hydrogen,  is  set  free  in  the  form  of  a  gas,  and  is  so  in- 
tensely heated  by  the  energy  of  the  chemical  action  that 
an  explosive  force  is  generated  sufficient  to  rend  the  rock 
in  pieces. 

Thus  the  philosophy  of  detonations  and  explosions  is,  in 
general,  simply  this,  namely,  that  substances  having  a  very 
powerful  tendency  to  combine  are  brought  together  un- 
der such  conditions  that  this  tendency  may  be  suddenly 
set  free  to  act ;  then  the  particles  of  which  the  substances 
are  composed  fall  together,  as  it  were,  with  enormous  force, 
though  it  is  a  force  acting  through  very  minute  distances 
as  estimated  by  our  senses.  In  thus  falling,  and  by  the 
sudden  arrest  of  the  force  with  which  they  fall,  they  gen- 
erate very  intense  heat,  and  this  heat,  acting  through  the 
gases  which  are  likewise  usually  also  set  free  by  the  ac- 
tion, develop  an  enormous  expansive  force,  which,  sudden- 
ly breaking  loose  from  the  restraints  confining  it,  produces 
the  disruptive  effect,  while  the  shock  communicated  to  the 
air  produces  the  sound ;  these  together  constitute  the  ex- 
plosion. 


HOW   TIME   IS  TO   BE  TAKEN   INTO   ACCOUNT.          289 


CHAPTER  XVH. 

FORCE    IN   RELATION   TO   TIME. 

THERE  are  some  very  interesting  and  important  consid- 
erations involved  in  the  relation  between  time  and  force — 
considerations  which  are  necessary  to  be  taken  into  ac- 
count in  order  to  the  attainment  of  clear  and  correct  ideas 
of  the  fundamental  principles  involved  in  the  subject. 

In  estimating  absolute  quantities  of  force,  the  element 
of  time  is  not  necessarily  to  be  taken  into  account  at  all, 
though  at  first  thought  people  are  generally  apt  to  imag- 
ine it  otherwise.  But  the  amount  of  force  expended  in 
raising  one  pound  one  foot  is  an  absolute  and  definite 
quantity,  whether  more  or  less  time  is  expended  in  produ- 
cing it. 

A  gallon  of  water  is  the  same  quantity  whether  it  falls 
drop  by  drop  and  is  half  a  day  in  accumulating,  or  flows 
in  a  gushing  stream  so  as  to  fill  the  measm-e  in  a  minute. 
In  the  same  manner  a  foot-pound  is  a  foot-pound,  neither 
more  nor  less,  whether  it  is  the  work  of  a  squirrel  raising 
the  pound  slowly  and  laboriously  by  a  cord  wound  round 
an  axle  connected  with  his  revolving  cage,  or  is  a  part  of 
the  immense  energy  expended  in  raising,  in  five  seconds, 
by  steam,  a  trip-hammer  weighing  many  tons. 

When  we  say  that  a  horse  is  five  or  seven  times  stronger 
than  a  man,  we  mean  that  he  can  exert  a  force  in  one  hour 
equal  to  that  which  a  man  can  exert  in  five  or  seven  hours. 
The  theoretical  horse-power — that  by  which  the  efficiency 
of  powerful  engines  is  estimated — is  33,000  foot-pounds  per 
N 


2UO  FORCE    IK   RELATION   TO   TIME. 

minute  ;*  bat  every  one  of  those  foot-pounds  represents  a 
quantity  of  force  precisely  equal  to  that  exerted  by  the 
squirrel  in  raising  a  pound  weight  one  foot,  or  an  ounce 
weight  sixteen  feet,  or,  if  we  can  imagine  such  a  thing, 
that  exerted  by  a  flea  trained  to  work  in  a  mimic  tread- 
mill, and  raising  thereby  a  weight  of  one  grain  as  many 
feet  as  there  are  grains  in  a  pound. 

Thus,  in  simply  estimating  quantities  of  force,  the  ele- 
ment of  time  is  not  at  all  concerned,  just  as  in  estimating 
any  absolute  quantity  of  water  we  have  nothing  to  do  with 
the  time  that  was  required  for  it  to  flow  through  a  particu- 
lar faucet ;  but  in  estimating  the  amount  offeree  which  can 
be  obtained  from  particular  sources  of  power,  we  have  to 
consider  the  element  of  time,  in  order  to  determine  the  ef- 
fectual value  of  the  results.  Just  as  in  the  case  of  water, 
though  a  gallon  is  a  gallon,  neither  more  nor  less,  however 
slowly  or  rapidly  it  may  come,  we  have  to  consider  how 
many  gallons  a  given  source  will  supply  in  a  given  time, 
in  order  to  make  our  calculations  correctly  in  respect  to 
what  can  be  done  with  it. 

There  are  two  respects  in  which  the  element  of  time 
comes  into  the  account  in  calculations  relating  to  the  em- 
ployment of  force.  First,  the  rapidity  with  which  the  force 
is  either  brought  into  action  from  its  latent  state,  or  can 
be  delivered  to  the  control  of  man ;  and,  secondly,  the  ra- 
pidity with  which  it  can  be  transmitted  from  place  to  place. 
In  respect  to  the  first  point,  in  the  burning  of  coal  under 
the  boiler  of  a  steam-engine,  force  is  developed  by  coming 
from  a  latent  into  an  active  state ;  and  in  the  case  of  a  mill- 
wheel  carried  by  a  stream  of  water,  the  force  is  already  in 
action,  but  is  delivered,  or,  rather,  a  portion  of  it  is  deliv- 

*  This  would  be  about  what  he  would  do  by  walking  off  at  the  rate  vf 
one  step  two  feet  long  for  every  second,  and  raising  by  means  of  a  rope 
passing  over  pulleys  a  weight  of  270  pounds. 


VARIOUS   BATES   OF  TRANSMISSION.  291 

ered  through  the  mill-wheel  to  the  control  of  man.  It  is,  of 
course,  important  to  consider  how  much  force  such  sources 
of  supply  would  furnish  in  a  given  time. 

And,  secondly,  if  the  force  so  furnished  is  to  be  trans- 
mitted from  one  place  to  another,  either  by  water-pipes,  or 
air-pipes,  or  wires,  or  bands,  it  is  often  necessary  to  con- 
sider the  time  which  will  be  required  for  such  transmission. 

It  is  surprising  ho\v  great  a  difference  there  is  in  the  ra- 
pidity with  which  force,  in  its  various  forms  and  through 
different  media,  can  be  transmitted.  We  have  a  good  il- 
lustration of  this  in  the  case  of  the  eruptions  of  Vesuvius 
which  are  taking  place  on  so  remarkable  a  scale  at  the 
time  of  this  present  writing.  Let  us  see  at  what  different 
rates  of  speed  the  forces  that  are  set  in  motion  by  any  one 
of  the  explosions  that  take  place  are  transmitted  to  differ- 
ent distances  from  the  spot.  First,  if  we  suppose  the  dis- 
tance from  the  crater  to  Naples  through  the  air  is  ten 
miles,  a  bird,  frightened  by  the  thundering  report  and  the 
burst  of  vapor  and  flame,  would  fly  to  the  city  in  ten  min- 
utes, the  sound  of  the  explosion  would  traverse  the  inter- 
vening air  in  perhaps  a  minute  and  a  half,  and  the  light 
of  the  flash  in  about  T^.WTT  °f  one  second,  a  speed  that  is 
altogether  inconceivable  to  us. 

And  yet  all  these  different  modes  of  communication  are 
only  examples  of  the  transmission  of  force  in  different 
forms,  the  first  impulse  being  given  in  each  case  by  the 
explosion. 

It  is  impossible  for  us  to  form  any  conception  of  the 
velocity  of  such  a  motion  as  that  of  light,  nor  picture  to 
our  imagination  any  kind  of  undulation  as  moving  at  such 
a  rate. 

We  can,  however,  gain  some  idea  of  the  nature  of  such 
a  motion  by  attempting  to  form  some  definite  conception 
of  the  manner  in  which  motion  must  pass  through  any 


292  FOKCE    IN   RELATION   TO   TIME. 

elastic  substance.  Suppose,  for  instance,  we  have  a  long 
elastic  cord  or  line,  like  an  India-rubber  tube,  except  that 
its  being  hollow  would  be  of  no  consequence,  and  that  two 
persons  are  experimenting  with  it,  one  having  hold  of  each 
end.  Now  if  the  person  at  one  end  gives  a  sudden  pull, 
the  motion  will  be  communicated  from  that  end  to  the 
other  in  this  way,  as  is  supposed,  namely,  the  particles  of 
the  India-rubber  next  the  person's  hand  that  pulls  will,  by 
their  attraction  for  those  next  beyond,  draw  them  in  the 
direction  in  which  they  themselves  have  been  pulled,  and 
they  the  next,  and  so  on  by  a  kind  of  wave  or  undulation 
of  motion  from  one  end  of  the  line  to  the  other. 

It  would  be  substantially  the  same  in  the  case  of  pushing, 
provided  that  the  line  could  be  prevented  from  bending 
laterally. 

It  is  supposed  that  the  motion  is  communicated  in  a 
somewhat  similar  way,  only  with  inconceivably  greater 
rapidity,  in  the  case  of  a  pull  or  a  push  communicated 
through  an  iron  wire,  or  through  any  other  solid  sub- 
stance— that  is,  that  one  set  of  particles  communicates  its 
motion  to  the  next,  and  the  second  set  to  the  third,  and  so 
on  to  the  end ;  and,  of  course,  that  all  such  transmissions  of 
motion  require  a  certain  portion  of  time,  however  minute, 
and  that  the  period  required  is  in  proportion  to  the  distance 
passed  over. 

The  reader  will  perceive,  on  a  moment's  reflection,  that 
undulations  or  vibrations  of  this  kind  are  very  different 
from  those  of  waves  in  water,  in  this  respect,  namely,  that 
the  direction  of  the  motion  of  the  particles  is  backward  and 
forward  instead  of  being  upward  and  downward.  There 
is,  however,  a  striking  analogy  between  the  two  different 
modes. 

If  this  is  the  true  theory  of  the  transmission  of  the  solar 
radiation,  for  example,  we  may  well  be  amazed  at  the  in- 


TRANSMISSION   OF   ELECTRIC   FORCE.  293 

conceivable  capabilities  of  nature  in  respect  to  the  phe- 
nomena of  force.  The  distance  from  the  earth  to  the  sun 
is  so  great  that  it  would  require  300  years  for  a  railroad 
train  at  full  speed  to  traverse  it,  and  yet  the  undulations 
of  light  pass  over  it  in  eight  minutes  and  a  half. 

And  then,  on  the  other  hand,  the  magnitude  of  the  dis- 
tances that  the  human  mind  has  to  take  cognizance  of  in 
the  visible  universe  is  not  less  amazing  than  the  rapidity 
of  the  action  taking  place  in  it ;  for,  though  light  would 
pass  in  less  than  ten  minutes  from  the  sun  to  the  earth, 
there  are  stars  known  to  be  so  remote  that  it  would  require 
something  like  a  thousand  years  for  the  light  coming  from 
them  to  reach  us  when  proceeding  at  the  same  rate  of  mo- 
tion— that  is,  at  a  rate  which  would  traverse  a  distance  in 
about  eight  minutes  which  it  would  take  a  railroad  train 
300  years  to  pass  over,  though  going  at  full  speed. 

Electricity,  as  it  manifests  itself  in  passing  along  the  tele- 
graph wire,  is  supposed  to  be  a  force  in  process  of  being 
transmitted  in  the  form  of  some  kind  of  vibratory  or  un- 
dulatory  motion,  either  of  the  substance  of  the  wire  itself, 
or  of  some  subtle  medium  contained  in  it.  This  is  inferred 
from  the  fact  that  a  certain  amount  of  force  in  some  form 
or  other  must  be  expended  at  one  end  of  the  wire,  and  the 
same  amount  in  some  other  form  is,  or  may  be,  developed 
from  it  at  the  other  end.  The  force  thus  necessary  at  the 
beginning  is  usually  generated  by  a  process  something  like 
combustion,  in  wrhich  zinc,  or  some  other  metal,  takes  the 
place  of  fuel ;  that  is  to  say,  the  process  is  like  combustion 
in  the  fact  that  it  consists  of  a  powerful  recombination  of 
the  metal  with  oxygen  previously  separated  from  it,  only 
the  combination  takes  place  under  such  circumstances  that 
the  liberated  force  reappears  in  the  form  of  electricity  in- 
stead of  in  that  of  light  and  heat. 

But  there  must  always  be  an  expenditure  of  force  in 


294  FOBCE   IN   RELATION   TO  TIME. 

some  form  to  set  the  electric  current  in  motion.  This  force, 
as  has  already  been  said,  is  supplied  generally  by  a  battery 
at  one  end  of  the  line ;  but  when  a  special  current  has  to 
be  sent  from  any  intermediate  point,  for  any  special  pur- 
pose, a  new  force  must  be  imparted  by  an  apparatus  for 
consuming  an  additional  quantity  of  zinc  fuel,  if  it  may  be 
so  called.  The  engraving  represents  the  manner  in  which 
this  is  done,  or  was  formerly  done,  in  some  countries  in 
Europe.  An  accident  has  happened  to  the  train,  and  the 
official  wishes  to  communicate  the  knowledge  of  the  fact 
to  the  next  station.  He  has  in  his  hand  a  small  battery 
inclosed  in  a  box.  By  a  slight  movement  of  the  handle 
he  sets  the  battery  in  action.  The  oxygen  begins  to  com- 
bine with  the  zinc,  thus  restoring,  as  it  were,  the  force  with 
which  the  two  elements  were  originally  separated  from 
each  other.  This  force  appears  in  the  form  of  electricity, 
and  the  man,  by  means  of  a  conductor  attached  to  a  long, 
slender  pole,  communicates  the  force  to  one  of  the  wires, 
and  thus  can  send  a  series  of  impulses  to  the  nearest  station. 

He  can  not  communicate  a  message  of  words  convenient- 
ly in  this  way,  but  he  can  call  attention  and  procure  help 
somewhat  as  a  person  sick  in  a  chamber  can  call  for  help 
by  knocking  on  the  floor  under  circumstances  in  which 
he  would  not  be  able  to  communicate  any  information  in 
words. 

This  method,  however,  is  now  seldom  used  on  any  rail- 
road, other  more  convenient  ones  having  superseded  it ; 
but  it  will  illustrate  the  principle  which  I  have  been  ex- 
plaining. 

The  word  force  is  used  in  several  very  different  senses  in 
common  parlance.  The  import  of  the  word,  for  example, 
is  very  different  as  used  in  the  phrases  force  of  gravitation, 
force  of  cohesion,  and  other  similar  expressions,  from  that 
which  is  implied  when  we  speak  of  the  force  of  a  current 


TRANSMITTING   AN   IMPULSE   OF   FOECE. 


EE  ACTION.  297 

of  water  or  of  wind.  Indeed,  some  writers  have  maintained 
that,  on  account  of  this  ambiguity,  the  word  force  ought  to 
be  banished  from  all  scientific  discussions,  and  the  word 
energy  substituted,  to  denote  that  form  offeree  which  com- 
municates itself  in  some  kind  of  motion  from  one  body  to 
another,  and  expends  itself  in  the  one  just  in  proportion  as 
it  passes  into  the  other.  It  is  force  in  this  sense  which  has 
been  chiefly  treated  of  in  this  volume — that  is,  force  in  the 
sense  of  energy,  which  is  diminished  in  one  body  just  in 
proportion  as  it  is  imparted  to  another. 

And  the  portion,  too,  it  must  be  remembered,  which  is 
lost  by  one  is  precisely  that  which  is  gained  by  the  other. 
Let  a  log  be  rolled  from  the  bank  of  a  river  into  the  water, 
and  the  flow  of  the  current  will  soon  set  it  in  motion  down 
the  stream ;  but  just  so  far  as  motion  is  imparted  to  the  log, 
just  to  that  precise  degree  that  of  the  water  that  impinges 
upon  it  is  diminished ;  that  is,  the  motion  of  the  water  is 
retarded  just  as  much  as  the  log  is  impelled,  so  that  the 
whole  amount  of  motion  is  the  same  as  before. 

And,  in  the  same  manner,  a  vessel  at  sea  is  driven  forward 
only  so  fast  as  the  wind  itself  is  kept  back  by  it ;  that  is, 
the  wind  can  not  give  up  its  energy  and  keep  it  too.  This 
is  true  in  cases  of  oblique  as  well  as  of  direct  action,  as,  for 
example,  in  the  case  of  a  windmill,  or  a  vessel  sailing  on  a 
wind,  as  they  say,  in  which  cases  the  wind  strikes  the  sails 
obliquely,  and  moves  them  forward  by  an  indirect  reaction. 

It  is  only  just  so  far  as  the  wind  itself,  or  a  portion  of  it, 
is  retarded  in  its  motion  in  one  direction  that  the  vessels 
are  made  to  move  in  another ;  that  is,  the  force  or  energy 
is  not  produced;  it  is  only  parted  with  by  one  body  to  be 
received  by  another. 

It  is  thus  only  a  small  part  of  the  moving  force  or  energy 
that  man  withholds  from  the  wind  by  the  sails  of  his  ships, 
or  of  his  windmills  by  his  sails,  or  from  the  current  of  a 


FOKCE   IN    RELATION   TO   TIME. 


OBLIQUE  ACTION. 

river  by  his  water-wheels.  Perhaps  the  greatest  force  that 
man  has  wholly  under  his  control  is  that  drawn  from  coal, 
and  kept  under  subjection  and  guidance  in  the  large  steam- 
engines  that  he  builds.  The  British  government  have  re- 
cently constructed  some  war  steamers  of  a  very  large  class, 
one  of  which,  the  Devastation,  has  engines  of  5600  horse 
power.  Think  of  a  team  of  horses  four  abreast,  and  more 
than  two  miles  long — for  that  would  be  about  the  space 
that  such  a  power  represented  by  horses  would  require — 
and  all  entirely  under  the  perfect  control  and  management 
of  one  man,  so  that  it  can  be  made  to  obey  orders  commu- 
nicated by  the  slightest  signals  of  the  officer  of  the  deck — 


MINUTE   FOKCES. 


299 


signals  made  by  the  motion  of  the  fingers  of  his  hand  to 
"  Ease  her,"  "  Back  her,"  "  Stop  her,"  and  the  like — with  the 
promptness,  and,  at  the  same  time,  with  the  self-restraint 
of  the  most  docile  dog ;  and  then  again,  at  the  word,  or, 
rather,  the  touch  of  command,  can  be  made  to  urge  the 
mighty  mass  of  the  ship,  with  its  immense  weight  of  iron 
plating,  and  its  enormous  guns,  and  its  hundreds  of  work- 
ing population,  against  the  strongest  gales  and  through 
the  heaviest  surges  with  irresistible  energy. 

On  the  other  hand,  the  smallest  forces  which  man  takes 
definite  cognizance  of  and  measures  are  perhaps  those  de- 
veloped by  the  faintest  currents  of  electricity.  The  instru- 
ment by  which  such  feeble  forces  are  measured  is  called 
the  Torsion  Balance. 


300  FOECE    IN   KELATION   TO   TIME. 

It  is  called  the  Torsion  Balance  because  the  force  with 
which  that  of  the  current  is  brought  into  comparison  is  the 
resistance  to  the  torsion  or  twisting  of  some  very  delicate 
fibre,  usually  a  single  filament  of  a  spider's  or  a  silk-worm's 
spinning.  The  engraving  shows  the  form  and  general  ap- 
pearance of  the  instrument.  It  is  inclosed  in  glass,  to  pro- 
tect the  needle  within  from  currents  of  air.  It  stands  on 
a  tripod  furnished  with  screws  to  secure  a  perfectly  level 
position  for  it.  The  current  of  electricity  is  brought  by 
one  of  the  wires  on  the  left,  and  carried  away  by  the  other. 
The  receiving  wire,  after  entering  beneath  the  instrument, 
is  wound  round  a  coil,  a  portion  of  which  is  visible  in  the 
engraving.  By  this  means  the  magnetic  effect  which  such 
a  current  is  capable  of  producing  is  greatly  increased. 
This  magnetic  influence,  acting,  through  the  circular  plate 
above  it,  upon  the  needle  suspended  by  the  filament,  causes 
it  to  turn  in  one  direction  or  the  other,  its  turning  being 
resisted  by  the  torsion  of  the  filament,  and  the  degree  of 
it,  as  marked  by  the  gradation  of  the  circle,  denoting  the 
strength  of  the  current. 

By  this  instrument  forces  inconceivably  minute  may  be 
measured  and  compared. 

The  doctrine  that  lies  at  the  foundation  of  the  science  of 
force — that,  namely,  which  it  has  been  the  main  object  of 
this  book  to  explain  and  illustrate,  is  this :  that  no  force,  in 
the  sense  of  energy,  can  ever  be  generated,  but  can  only, 
when  already  existing,  either  in  an  active  or  suspended 
form,  be  transmitted  or  released,  each  particular  movement 
of  it  requiring  a  certain  lapse  of  time.  The  cases  which 
seem  at  first  view  to  be  exceptions  to  this  principle  are  all 
illusory,  as,  for  example,  that  of  the  explosion  of  a  blast 
of  gunpowder  rending  rocks  in  pieces  by  the  communica- 
tion of  a  very  small  force  through  an  electric  wire.  Here 
the  great  force  which  the  small  one  seems  to  produce  is 


THE    KOW    OP   BRICKS.  301 

not  generated)  but  only  catted  out  into  action.  The  true 
source  of  the  disrupting  power  is  in  the  sun,  which  sepa- 
rated the  oxygen  from  the  carbon  by  the  actinic  force  of 
its  rays  when  the  wood  which  furnished  the  carbon  for  the 
gunpowder  was  growing.  The  carbon  and  the  oxygen 
being  placed  side  by  side  in  the  gunpowder,  with  an  im- 
mensely strong  tendency  to  come  together — which  tenden- 
cy can,  however,  for  some  mysterious  reason,  only  come 
into  action  when  a  portion  of  them  is  raised  to  the  right 
temperature — the  spark  produced  by  the  electric  discharge 
acts,  not  to  generate  the  force,  but  only  to  release  it  from  its 
suspense  and  detention.  It  is  in  principle  a  case  precisely 
analogous  to  that  of  a  child  who  sets  to  falling  a  long  row 
of  bricks  by  a  touch  upon  one  of  them  at  the  end.  The 
whole  amount  of  force  with  which  the  bricks  fall  is  very 
great  compared  with  that  of  the  touch  with  which  the 
whole  movement  was  begun ;  but  it  is  force  which  was 
accumulated  in  the  bricks,  as  it  were,  by  the  labor  of  the 
child  in  setting  them  up  one  by  one — in  lifting  each  one  up 
far  enough  to  set  it  on  the  end.  Thus  the  force  with  which 
the  bricks  fell  was  only  an  accumulated  force  released,  and 
not  a  new  force  generated  by  the  slight  touch  which  set 
the  train  in  motion. 

And  just  as  in  the  movement  transmitted  through  such 
a  train  a  certain  time  is  required  for  the  movement  to  pass 
onward  to  the  end  of  it,  so  in  all  cases  a  definite  lapse  of 
time  is  expended  in  every  mode  by  which  force  is  trans- 
mitted— sound  passing  through  the  air  requiring  but  lit- 
tle, electricity  through  a  wire  very  much  less,  and  light 
through  the  luminiferous  ether,  which  is  supposed  to  be 
the  medium  that  conveys  it,  the  least  of  all. 


CONCLUSION. 


CHAPTER  XVIIL 

CONCLUSION. 

THE  concluding  limit  of  the  space  within  which  the  dis- 
cussion of  each  subject  in  these  volumes  is  necessarily  con- 
fined now  draws  near,  and  warns  me  that  I  must  bring 
what  I  have  to  say  upon  Force  to  a  close.  This  is  not, 
however,  because  the  subject  is  exhausted.  All  that  has 
been  said  in  this  volume,  and,  indeed,  all  that  man  has  yet 
learned,  and,  in  fact,  all  that  is  possible,  in  this  state  of  be- 
ing, for  him  to  know,  forms  but  the  merest  beginning  of 
knowledge  in  this  boundless  field.  Every  young  man  who 
reads  this  book  attentively  will  find  that  he  knows  less, 
not  than  he  actually  did  know,  but  than  he  imagined  that 
he  knew  before  he  began  it;  for  the  field  of  knowledge 
on  this  subject  is  unbounded.  The  farther  we  enter  into 
it,  the  wider  the  region  beyond  us  expands,  but  then  the 
stronger  becomes  our  desire  to  go  on  and  explore  the  mys- 
teries that  remain,  so  that  the  effect  of  such  incipient 
studies  as  these  is  to  discourage  self-conceit,  not  weary  out 
the  love  of  knowledge. 

It  almost  always  surprises  the  learner  when  he  is  first 
informed  that  the  subject  of  force  really  includes  almost, 
if  not  all  the  phenomena  of  nature  that  are  subject  to  our 
cognizance.  But  this  is  strictly  true,  for  every  thing  that 
takes  place  is  a  manifestation  of  force  of  some  kind,  except, 
perhaps,  the  phenomena  involved  in  mental  operations. 
Many  scientific  men  would  not  even  except  those,  on  the 
ground  that  even  mental  operations,  so  far  as  they  mani- 
fest themselves  to  the  human  observation,  whether  they 


ENERGY    AND   PRESSURE.  303 

are  our  own  or  those  of  others,  act  through  and  by  means 
of  bodily  organs,  which  in  all  their  actions  are  dependent 
entirely  on  some  form  of  material  force  communicated  to 
the  system  in  the  food. 

However  this  may  be,  it  is  certain  that  all  which  takes 
place  in  the  visible  universe  around  us  consists  of  move- 
ment of  some  kind,  produced  by  some  previous  movement, 
and  thus  forming  a  part  of  the  grand  circuit  which  the 
vast  amount  of  cosmical  force — that  is,  the  force  that  is  in 
action  in  the  universe,  constantly  describes. 

Besides  this  moving  and  acting  force  called  energy, 
which  expends  itself,  or  rather  transmits  itself  in  its  action, 
there  is  what  is  sometimes  called  a  force,  namely,  pressure, 
which,  so  long  as  it  produces  no  motion,  undergoes  no 
change.  For  example,  if  a  heavy  weight  is  supported  in 
the  air  on  the  top  of  a  tall  pillar  of  wood,  like  a  mast,  and 
remains  at  rest,  it  will  continue  to  exert  the  same  pressure 
upon  the  fibres  of  the  wood  forever  without  any  change. 
So  long  as  there  is  no  movement  there  is  no  expenditure, 
and  the  pressure  remains  undiminished.  But  if  the  pillar 
be  suddenly  removed,  the  weight  begins  to  descend,  pass- 
ing through  space  and  occupying  time;  and  the  force  be- 
gins to  be  expended — that  is,  transmitted  to  the  surround- 
ing objects  which  it  meets  on  its  way,  or  encounters  at  the 
end  of  its  descent.  It  is  this  force,  acting  in  time  and 
through  distance,  which  is  called  energy,  and  has  been  the 
main  subject  of  discussion  in  this  volume. 

Lawrence  explained  all  these  things  pretty  clearly  and 
fully  to  John  in  his  various  conversations  with  him,  and 
somewhat  more  in  detail  than  they  have  been  stated  here. 
He  also,  from  time  to  time,  stated  and  explained  particular 
facts  to  Rick,  as  he  had  occasion  to  see  him,  but  without 
much  attempt  to  make  him  understand  abstract  principles 
or  extended  generalizations.  Such  a  boy  must  be  taught 


304  CONCLUSION. 

particulars  in  respect  to  the  phenomena  of  nature  for  a 
long  time  before  he  is  prepared  to  see  the  analogies  which 
connect  them  together,  or  to  comprehend  the  general  prin- 
ciples that  underlie  them  all.  Lawrence  had  too  much 
knowledge  of  the  nature  and  movements  of  a  mind  like 
Rick's,  which  is  in  process  of  formation,  to  attempt  too 
much  with  it,  so  he  was  satisfied  with  calling  Rick's  at- 
tention to  such  points  as  could  be  made  obvious  through 
the  senses.  A  boy  of  his  age  can  much  more  easily  under- 
stand, and  will  much  more  fully  appreciate  what  he  can 
see,  or  picture  to  his  imagination  in  the  form  of  a  visible 
phenomenon,  than  things  which  exist  in  his  mind  only  as  a 
thought. 

But  the  great  effect  produced  on  Rick's  mind  by  Law- 
rence's instructions  was,  after  all,  a  moral  one — that  is,  it 
was  the  influence  of  them  upon  his  feelings  and  affections. 
While  he  hated  most  of  the  teachers  under  whose  care  he 
had  been  successively  placed — teachers  who  took  appar- 
ently no  notice  when  he  did  right,  but  scolded  or  whipped 
him  when  he  did  wrong — he  soon  began  to  form  a  strong 
attachment  for  Lawrence,  whom  he  readily  learned  to  con- 
sider as  his  friend ;  and  though  it  is  true  that  the  knowl- 
edge which  he  obtained  was  comparatively  slight,  and  of 
course,  like  the  beginnings  of  all  knowledge,  was  very  su- 
perficial, still  what  there  was  of  it  was  knowledge ;  and, 
what  was  better  than  all,  it  was  knowledge  acquired  with 
pleasure,  and  was  the  beginning  of  a  change  in  him,  which, 
if  it  should  be  followed  by  measures  and  treatment  of  a 
similar  character  by  the  teachers  of  theMorningside  School, 
would  probably,  in  time,  make  him  a  good  and  happy  boy. 

There  never  was  a  more  false  or  unphilosophical  senti- 
ment expressed  than  that  conveyed  by  Pope's  celebrated 
distich, 


FINAL    REFLECTIONS.  305 

"  A  little  learning  is  a  dangerous  thing ; 
Drink  deep,  or  taste  uot  the  Pierian  spring." 

If  such  a  doctrine  were  believed  and  obeyed,  it  would 
put  an  effectual  stop  to  all  acquisition  of  knowledge,  for  it 
is  only  a  "  little  learning"  on  any  conceivable  subject  that 
it  is  possible  for  any  one  in  the  present  condition  of  the 
human  mind  to  attain.  We  must  learn  all  we  can,  be  it 
little  or  a  great  deal,  on  every  subject  that  comes  within 
our  view.  We  may,  indeed,  make  a  choice  among  the  dif- 
ferent subjects  which  lie  open  before  us  in  regard  to  the 
degree  of  time  and  attention  which  we  will  devote  to  each, 
but  no  knowledge  is  useless  simply  because  it  is  but  a  be- 
ginning. 

There  are  thus  two  lessons  taught  by  this  book,  or,  rath- 
er, two  truths  to  be  learned  from  it : 

First,  that  physical  force  is  a  very  curious  and  interest- 
ing subject  of  study ;  and, 

Secondly,  that  it  may  be  made  one  excellent  means  of 
changing  the  heart  and  the  character  of  a  bad  boy ;  but 
that  the  way  to  employ  it  for  this  end  is  to  make  it  a  sub- 
ject of  curious  study  for  his  mind,  and  not  by  the  personal 
application  of  it  to  his  body. 


TUB    END. 


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REBER'S  HISTORY  OF  ANCIENT  ART.  History  of  Ancient 
Art.  By  Dr.  FRANZ  VON  REBER.  Revised  by  the  Author. 
Translated  and  Augmented  by  Joseph  Thacher  Clarke.  With 
310  Illustrations  and  a  Glossary  of  Technical  Terms.  8vo, 
Cloth,  $3  50. 

NEWCOMB'S  ASTRONOMY.  Popular  Astronomy.  By  SIMON 
NEWCOMB,  LL.D.  With  112  Engravings,  and  5  Maps  of  the 
Stars.  8vo,  Cloth,  $2  50  ;  School  Edition,  12mo,  Cloth,  $1  30. 

DA  VIS'S  INTERNATIONAL  LAW.  Outlines  of  International 
Law,  with  an  Account  of  its  Origin  and  Sources,  and  of  its  His- 
torical Development.  By  GEO.  B.  DAVIS,  U.S.A.,  Assistant 
Professor  of  Law  at  the  United  States  Military  Academy.  Crown 
8vo,  Cloth,  $2  00. 

CESNOL A'S  CYPRUS.  Cyprus :  its  Ancient  Cities,  Tombs,  and 
Temples.  A  Narrative  of  Researches  and  Excavations  during 
Ten  Years'  Residence  in  that  Island.  By  L.  P.  m  CESNOLA. 
With  Portrait,  Maps,  nnd  400  Illustrations.  8vo,  Cloth,  Extra, 
Uncut  Edges  and  Gilt  Tops,  $7  50. 

TENNYSON'S  COMPLETE  POEMS.  The  Complete  Poetical 
Works  of  Alfred,  Lord  Tennyson.  With  an  Introductory  Sketch 
by  Anne  Thackeray  Ritchie.  With  Portraits  and  Illustrations. 
8vo,  Extra  Cloth,  Bevelled,  Gilt  Edges,  $2  50. 

LEA'S  HISTORY  OF  THE  INQUISITION.  History  of  the  In- 
quisition of  the  Middle  Ages.  By  HENKT  CHARLES  LEA.  Three 
Volumes.  8vo,  Cloth,  Uncut  Edges  and  Gilt  Tops,  $3  00  per  vol. 

FLAMMARION'S  ATMOSPHERE.  Translated  from  the  French 
of  CAMILLE  FLAMMARION.  With  10  Chromo-Lithographs  and 
86  Vrjod-cuts.  8vo,  Cloth,  $6  00 ;  Half  Calf,  $8  25. 


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